2021-06-21 08:32:10

by SeongJae Park

Subject: [PATCH v31 00/13] Introduce Data Access MONitor (DAMON)

From: SeongJae Park <[email protected]>

Changes from Previous Version (v30)
===================================

Compared to the v30
(https://lore.kernel.org/linux-mm/[email protected]/),
this version contains below minor changes.

- Rebase on latest -mm tree (v5.13-rc6-mmots-2021-06-16-22-17)
- selftest: Fix wrong file content comparison (Markus Boehme)
- Collect 'Reviewed-by:' tags from Markus

Now all patches of this patchset has at least one 'Reviewed-by:' tags. Andrew,
could you please consider merging this into the -mm tree?

Introduction
============

DAMON is a data access monitoring framework for the Linux kernel. The core
mechanisms of DAMON called 'region based sampling' and 'adaptive regions
adjustment' (refer to 'mechanisms.rst' in the 11th patch of this patchset for
the detail) make it

- accurate (The monitored information is useful for DRAM level memory
management. It might not appropriate for Cache-level accuracy, though.),
- light-weight (The monitoring overhead is low enough to be applied online
while making no impact on the performance of the target workloads.), and
- scalable (the upper-bound of the instrumentation overhead is controllable
regardless of the size of target workloads.).

Using this framework, therefore, several memory management mechanisms such as
reclamation and THP can be optimized to aware real data access patterns.
Experimental access pattern aware memory management optimization works that
incurring high instrumentation overhead will be able to have another try.

Though DAMON is for kernel subsystems, it can be easily exposed to the user
space by writing a DAMON-wrapper kernel subsystem. Then, user space users who
have some special workloads will be able to write personalized tools or
applications for deeper understanding and specialized optimizations of their
systems.

DAMON is also merged in two public Amazon Linux kernel trees that based on
v5.4.y[1] and v5.10.y[2].

[1] https://github.com/amazonlinux/linux/tree/amazon-5.4.y/master/mm/damon
[2] https://github.com/amazonlinux/linux/tree/amazon-5.10.y/master/mm/damon

Long-term Plan
--------------

DAMON is a part of a project called Data Access-aware Operating System (DAOS).
As the name implies, I want to improve the performance and efficiency of
systems using fine-grained data access patterns. The optimizations are for
both kernel and user spaces. I will therefore modify or create kernel
subsystems, export some of those to user space and implement user space library
/ tools. Below shows the layers and components for the project.

---------------------------------------------------------------------------
Primitives: PTE Accessed bit, PG_idle, rmap, (Intel CMT), ...
Framework: DAMON
Features: DAMOS, virtual addr, physical addr, ...
Applications: DAMON-debugfs, (DARC), ...
^^^^^^^^^^^^^^^^^^^^^^^ KERNEL SPACE ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Raw Interface: debugfs, (sysfs), (damonfs), tracepoints, (sys_damon), ...

vvvvvvvvvvvvvvvvvvvvvvv USER SPACE vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
Library: (libdamon), ...
Tools: DAMO, (perf), ...
---------------------------------------------------------------------------

The components in parentheses or marked as '...' are not implemented yet but in
the future plan. IOW, those are the TODO tasks of DAOS project. For more
detail, please refer to the plans:
https://lore.kernel.org/linux-mm/[email protected]/

Evaluations
===========

We evaluated DAMON's overhead, monitoring quality and usefulness using 24
realistic workloads on my QEMU/KVM based virtual machine running a kernel that
v24 DAMON patchset is applied.

DAMON is lightweight. It increases system memory usage by 0.39% and slows
target workloads down by 1.16%.

DAMON is accurate and useful for memory management optimizations. An
experimental DAMON-based operation scheme for THP, namely 'ethp', removes
76.15% of THP memory overheads while preserving 51.25% of THP speedup. Another
experimental DAMON-based 'proactive reclamation' implementation, 'prcl',
reduces 93.38% of residential sets and 23.63% of system memory footprint while
incurring only 1.22% runtime overhead in the best case (parsec3/freqmine).

NOTE that the experimental THP optimization and proactive reclamation are not
for production but only for proof of concepts.

Please refer to the official document[1] or "Documentation/admin-guide/mm: Add
a document for DAMON" patch in this patchset for detailed evaluation setup and
results.

[1] https://damonitor.github.io/doc/html/latest-damon/admin-guide/mm/damon/eval.html

Real-world User Story
=====================

In summary, DAMON has used on production systems and proved its usefulness.

DAMON as a profiler
-------------------

We analyzed characteristics of a large scale production systems of our
customers using DAMON. The systems utilize 70GB DRAM and 36 CPUs. From this,
we were able to find interesting things below.

There were obviously different access pattern under idle workload and active
workload. Under the idle workload, it accessed large memory regions with low
frequency, while the active workload accessed small memory regions with high
freuqnecy.

DAMON found a 7GB memory region that showing obviously high access frequency
under the active workload. We believe this is the performance-effective
working set and need to be protected.

There was a 4KB memory region that showing highest access frequency under not
only active but also idle workloads. We think this must be a hottest code
section like thing that should never be paged out.

For this analysis, DAMON used only 0.3-1% of single CPU time. Because we used
recording-based analysis, it consumed about 3-12 MB of disk space per 20
minutes. This is only small amount of disk space, but we can further reduce
the disk usage by using non-recording-based DAMON features. I'd like to argue
that only DAMON can do such detailed analysis (finding 4KB highest region in
70GB memory) with the light overhead.

DAMON as a system optimization tool
-----------------------------------

We also found below potential performance problems on the systems and made
DAMON-based solutions.

The system doesn't want to make the workload suffer from the page reclamation
and thus it utilizes enough DRAM but no swap device. However, we found the
system is actively reclaiming file-backed pages, because the system has
intensive file IO. The file IO turned out to be not performance critical for
the workload, but the customer wanted to ensure performance critical
file-backed pages like code section to not mistakenly be evicted.

Using direct IO should or `mlock()` would be a straightforward solution, but
modifying the user space code is not easy for the customer. Alternatively, we
could use DAMON-based operation scheme[1]. By using it, we can ask DAMON to
track access frequency of each region and make
'process_madvise(MADV_WILLNEED)[2]' call for regions having specific size and
access frequency for a time interval.

We also found the system is having high number of TLB misses. We tried
'always' THP enabled policy and it greatly reduced TLB misses, but the page
reclamation also been more frequent due to the THP internal fragmentation
caused memory bloat. We could try another DAMON-based operation scheme that
applies 'MADV_HUGEPAGE' to memory regions having >=2MB size and high access
frequency, while applying 'MADV_NOHUGEPAGE' to regions having <2MB size and low
access frequency.

We do not own the systems so we only reported the analysis results and possible
optimization solutions to the customers. The customers satisfied about the
analysis results and promised to try the optimization guides.

[1] https://lore.kernel.org/linux-mm/[email protected]/
[2] https://lore.kernel.org/linux-api/[email protected]/

Comparison with Idle Page Tracking
==================================

Idle Page Tracking allows users to set and read idleness of pages using a
bitmap file which represents each page with each bit of the file. One
recommended usage of it is working set size detection. Users can do that by

1. find PFN of each page for workloads in interest,
2. set all the pages as idle by doing writes to the bitmap file,
3. wait until the workload accesses its working set, and
4. read the idleness of the pages again and count pages became not idle.

NOTE: While Idle Page Tracking is for user space users, DAMON is primarily
designed for kernel subsystems though it can easily exposed to the user space.
Hence, this section only assumes such user space use of DAMON.

For what use cases Idle Page Tracking would be better?
------------------------------------------------------

1. Flexible usecases other than hotness monitoring.

Because Idle Page Tracking allows users to control the primitive (Page
idleness) by themselves, Idle Page Tracking users can do anything they want.
Meanwhile, DAMON is primarily designed to monitor the hotness of each memory
region. For this, DAMON asks users to provide sampling interval and
aggregation interval. For the reason, there could be some use case that using
Idle Page Tracking is simpler.

2. Physical memory monitoring.

Idle Page Tracking receives PFN range as input, so natively supports physical
memory monitoring.

DAMON is designed to be extensible for multiple address spaces and use cases by
implementing and using primitives for the given use case. Therefore, by
theory, DAMON has no limitation in the type of target address space as long as
primitives for the given address space exists. However, the default primitives
introduced by this patchset supports only virtual address spaces.

Therefore, for physical memory monitoring, you should implement your own
primitives and use it, or simply use Idle Page Tracking.

Nonetheless, RFC patchsets[1] for the physical memory address space primitives
is already available. It also supports user memory same to Idle Page Tracking.

[1] https://lore.kernel.org/linux-mm/[email protected]/

For what use cases DAMON is better?
-----------------------------------

1. Hotness Monitoring.

Idle Page Tracking let users know only if a page frame is accessed or not. For
hotness check, the user should write more code and use more memory. DAMON do
that by itself.

2. Low Monitoring Overhead

DAMON receives user's monitoring request with one step and then provide the
results. So, roughly speaking, DAMON require only O(1) user/kernel context
switches.

In case of Idle Page Tracking, however, because the interface receives
contiguous page frames, the number of user/kernel context switches increases as
the monitoring target becomes complex and huge. As a result, the context
switch overhead could be not negligible.

Moreover, DAMON is born to handle with the monitoring overhead. Because the
core mechanism is pure logical, Idle Page Tracking users might be able to
implement the mechanism on thier own, but it would be time consuming and the
user/kernel context switching will still more frequent than that of DAMON.
Also, the kernel subsystems cannot use the logic in this case.

3. Page granularity working set size detection.

Until v22 of this patchset, this was categorized as the thing Idle Page
Tracking could do better, because DAMON basically maintains additional metadata
for each of the monitoring target regions. So, in the page granularity working
set size detection use case, DAMON would incur (number of monitoring target
pages * size of metadata) memory overhead. Size of the single metadata item is
about 54 bytes, so assuming 4KB pages, about 1.3% of monitoring target pages
will be additionally used.

All essential metadata for Idle Page Tracking are embedded in 'struct page' and
page table entries. Therefore, in this use case, only one counter variable for
working set size accounting is required if Idle Page Tracking is used.

There are more details to consider, but roughly speaking, this is true in most
cases.

However, the situation changed from v23. Now DAMON supports arbitrary types of
monitoring targets, which don't use the metadata. Using that, DAMON can do the
working set size detection with no additional space overhead but less
user-kernel context switch. A first draft for the implementation of monitoring
primitives for this usage is available in a DAMON development tree[1]. An RFC
patchset for it based on this patchset will also be available soon.

From v24, the arbitrary type support is dropped from this patchset because this
patchset doesn't introduce real use of the type. You can still get it from the
DAMON development tree[2], though.

[1] https://github.com/sjp38/linux/tree/damon/pgidle_hack
[2] https://github.com/sjp38/linux/tree/damon/master

4. More future usecases

While Idle Page Tracking has tight coupling with base primitives (PG_Idle and
page table Accessed bits), DAMON is designed to be extensible for many use
cases and address spaces. If you need some special address type or want to use
special h/w access check primitives, you can write your own primitives for that
and configure DAMON to use those. Therefore, if your use case could be changed
a lot in future, using DAMON could be better.

Can I use both Idle Page Tracking and DAMON?
--------------------------------------------

Yes, though using them concurrently for overlapping memory regions could result
in interference to each other. Nevertheless, such use case would be rare or
makes no sense at all. Even in the case, the noise would bot be really
significant. So, you can choose whatever you want depending on the
characteristics of your use cases.

More Information
================

We prepared a showcase web site[1] that you can get more information. There
are

- the official documentations[2],
- the heatmap format dynamic access pattern of various realistic workloads for
heap area[3], mmap()-ed area[4], and stack[5] area,
- the dynamic working set size distribution[6] and chronological working set
size changes[7], and
- the latest performance test results[8].

[1] https://damonitor.github.io/_index
[2] https://damonitor.github.io/doc/html/latest-damon
[3] https://damonitor.github.io/test/result/visual/latest/rec.heatmap.0.png.html
[4] https://damonitor.github.io/test/result/visual/latest/rec.heatmap.1.png.html
[5] https://damonitor.github.io/test/result/visual/latest/rec.heatmap.2.png.html
[6] https://damonitor.github.io/test/result/visual/latest/rec.wss_sz.png.html
[7] https://damonitor.github.io/test/result/visual/latest/rec.wss_time.png.html
[8] https://damonitor.github.io/test/result/perf/latest/html/index.html

Baseline and Complete Git Trees
===============================

The patches are based on the -mm tree. More specifically,
v5.13-rc6-mmots-2021-06-15-20-28 of https://github.com/hnaz/linux-mm. You can
also clone the complete git tree:

$ git clone git://github.com/sjp38/linux -b damon/patches/v31

The web is also available:
https://github.com/sjp38/linux/releases/tag/damon/patches/v31

Development Trees
-----------------

There are a couple of trees for entire DAMON patchset series and
features for future release.

- For latest release: https://github.com/sjp38/linux/tree/damon/master
- For next release: https://github.com/sjp38/linux/tree/damon/next

Long-term Support Trees
-----------------------

For people who want to test DAMON but using LTS kernels, there are another
couple of trees based on two latest LTS kernels respectively and containing the
'damon/master' backports.

- For v5.4.y: https://github.com/sjp38/linux/tree/damon/for-v5.4.y
- For v5.10.y: https://github.com/sjp38/linux/tree/damon/for-v5.10.y

Amazon Linux Kernel Trees
-------------------------

DAMON is also merged in two public Amazon Linux kernel trees that based on
v5.4.y[1] and v5.10.y[2].

[1] https://github.com/amazonlinux/linux/tree/amazon-5.4.y/master/mm/damon
[2] https://github.com/amazonlinux/linux/tree/amazon-5.10.y/master/mm/damon

Git Tree for Diff of Patches
============================

For easy review of diff between different versions of each patch, I prepared a
git tree containing all versions of the DAMON patchset series:
https://github.com/sjp38/damon-patches

You can clone it and use 'diff' for easy review of changes between different
versions of the patchset. For example:

$ git clone https://github.com/sjp38/damon-patches && cd damon-patches
$ diff -u damon/v30 damon/v31

Sequence Of Patches
===================

First three patches implement the core logics of DAMON. The 1st patch
introduces basic sampling based hotness monitoring for arbitrary types of
targets. Following two patches implement the core mechanisms for control of
overhead and accuracy, namely regions based sampling (patch 2) and adaptive
regions adjustment (patch 3).

Now the essential parts of DAMON is complete, but it cannot work unless someone
provides monitoring primitives for a specific use case. The following two
patches make it just work for virtual address spaces monitoring. The 4th patch
makes 'PG_idle' can be used by DAMON and the 5th patch implements the virtual
memory address space specific monitoring primitives using page table Accessed
bits and the 'PG_idle' page flag.

Now DAMON just works for virtual address space monitoring via the kernel space
api. To let the user space users can use DAMON, following four patches add
interfaces for them. The 6th patch adds a tracepoint for monitoring results.
The 7th patch implements a DAMON application kernel module, namely damon-dbgfs,
that simply wraps DAMON and exposes DAMON interface to the user space via the
debugfs interface. The 8th patch further exports pid of monitoring thread
(kdamond) to user space for easier cpu usage accounting, and the 9th patch
makes the debugfs interface to support multiple contexts.

Three patches for maintainability follows. The 10th patch adds documentations
for both the user space and the kernel space. The 11th patch provides unit
tests (based on the kunit) while the 12th patch adds user space tests (based on
the kselftest).

Finally, the last patch (13th) updates the MAINTAINERS file.

Patch History
=============

Changes from v30
(https://lore.kernel.org/linux-mm/[email protected]/)
- Rebase on latest -mm tree (v5.13-rc6-mmots-2021-06-16-22-17)
- selftest: Fix wrong file content comparison (Markus Boehme)
- Collect 'Reviewed-by:' tags from Markus

Changes from v29
(https://lore.kernel.org/linux-mm/[email protected]/)
- Rebase on latest -mm tree (v5.13-rc6-mmots-2021-06-15-20-28)
- Remove unnecessary documents
- Wordsmith commit message for PAGE_IDLE separation (Amit Shah)
- selftests: Fix shellcheck warnings and cleanup (Maximilian Heyne)
- Wordsmith the document (Markus Boehme)
- Fix a typo in comments (Fernand Sieber)
- Collect 'Reviewed-by:' tags from "Fernand Sieber <[email protected]>"

Changes from v28
(https://lore.kernel.org/linux-mm/[email protected]/)
- Rebase on latest -mm tree (v5.13-rc1-mmots-2021-05-13-17-23)

Changes from v27
(https://lore.kernel.org/linux-mm/[email protected]/)
- Rebase on latest -mm tree (v5.12-rc7-mmots-2021-04-11-20-49)
- dbgfs: Fix wrong failure handlings (Stefan Nuernberger)
- dbgfs: Change return type of 'dbgfs_fill_ctx_dir()' to void (Greg KH)

Changes from v26
(https://lore.kernel.org/linux-mm/[email protected]/)
- Rebase on latest -mm tree (v5.12-rc6-mmots-2021-04-06-22-33)
- Check kmalloc() failures in dbgfs init (Greg KH)
- Fix a typo: s/stollen/stolen/ (Stefan Nuernberger)
- Update document for updated user space tool path

Changes from v25
(https://lore.kernel.org/linux-mm/[email protected]/)
- Rebase on latest -mm tree (v5.12-rc4-mmots-2021-03-28-16-40)
- Remove unnecessary test code that dependent on record feature
- Handle special mappings having no corresponding 'struct page' (Guoju Fang)

Please refer to the v25 patchset to get older history.

SeongJae Park (13):
mm: Introduce Data Access MONitor (DAMON)
mm/damon/core: Implement region-based sampling
mm/damon: Adaptively adjust regions
mm/idle_page_tracking: Make PG_idle reusable
mm/damon: Implement primitives for the virtual memory address spaces
mm/damon: Add a tracepoint
mm/damon: Implement a debugfs-based user space interface
mm/damon/dbgfs: Export kdamond pid to the user space
mm/damon/dbgfs: Support multiple contexts
Documentation: Add documents for DAMON
mm/damon: Add kunit tests
mm/damon: Add user space selftests
MAINTAINERS: Update for DAMON

Documentation/admin-guide/mm/damon/index.rst | 15 +
Documentation/admin-guide/mm/damon/start.rst | 114 +++
Documentation/admin-guide/mm/damon/usage.rst | 112 +++
Documentation/admin-guide/mm/index.rst | 1 +
Documentation/vm/damon/api.rst | 20 +
Documentation/vm/damon/design.rst | 166 ++++
Documentation/vm/damon/faq.rst | 51 ++
Documentation/vm/damon/index.rst | 30 +
Documentation/vm/index.rst | 1 +
MAINTAINERS | 12 +
include/linux/damon.h | 265 +++++++
include/linux/page-flags.h | 4 +-
include/linux/page_ext.h | 2 +-
include/linux/page_idle.h | 6 +-
include/trace/events/damon.h | 43 ++
include/trace/events/mmflags.h | 2 +-
mm/Kconfig | 10 +
mm/Makefile | 1 +
mm/damon/Kconfig | 69 ++
mm/damon/Makefile | 5 +
mm/damon/core-test.h | 253 ++++++
mm/damon/core.c | 718 ++++++++++++++++++
mm/damon/dbgfs-test.h | 126 +++
mm/damon/dbgfs.c | 615 +++++++++++++++
mm/damon/vaddr-test.h | 328 ++++++++
mm/damon/vaddr.c | 623 +++++++++++++++
mm/page_ext.c | 12 +-
mm/page_idle.c | 10 -
tools/testing/selftests/damon/Makefile | 7 +
.../selftests/damon/_chk_dependency.sh | 28 +
.../testing/selftests/damon/debugfs_attrs.sh | 75 ++
31 files changed, 3706 insertions(+), 18 deletions(-)
create mode 100644 Documentation/admin-guide/mm/damon/index.rst
create mode 100644 Documentation/admin-guide/mm/damon/start.rst
create mode 100644 Documentation/admin-guide/mm/damon/usage.rst
create mode 100644 Documentation/vm/damon/api.rst
create mode 100644 Documentation/vm/damon/design.rst
create mode 100644 Documentation/vm/damon/faq.rst
create mode 100644 Documentation/vm/damon/index.rst
create mode 100644 include/linux/damon.h
create mode 100644 include/trace/events/damon.h
create mode 100644 mm/damon/Kconfig
create mode 100644 mm/damon/Makefile
create mode 100644 mm/damon/core-test.h
create mode 100644 mm/damon/core.c
create mode 100644 mm/damon/dbgfs-test.h
create mode 100644 mm/damon/dbgfs.c
create mode 100644 mm/damon/vaddr-test.h
create mode 100644 mm/damon/vaddr.c
create mode 100644 tools/testing/selftests/damon/Makefile
create mode 100644 tools/testing/selftests/damon/_chk_dependency.sh
create mode 100755 tools/testing/selftests/damon/debugfs_attrs.sh

--
2.17.1

2021-06-21 08:32:20

by SeongJae Park

Subject: [PATCH v31 01/13] mm: Introduce Data Access MONitor (DAMON)

From: SeongJae Park <[email protected]>

DAMON is a data access monitoring framework for the Linux kernel. The
core mechanisms of DAMON make it

- accurate (the monitoring output is useful enough for DRAM level
performance-centric memory management; It might be inappropriate for
CPU cache levels, though),
- light-weight (the monitoring overhead is normally low enough to be
applied online), and
- scalable (the upper-bound of the overhead is in constant range
regardless of the size of target workloads).

Using this framework, hence, we can easily write efficient kernel space
data access monitoring applications. For example, the kernel's memory
management mechanisms can make advanced decisions using this.
Experimental data access aware optimization works that incurring high
access monitoring overhead could again be implemented on top of this.

Due to its simple and flexible interface, providing user space interface
would be also easy. Then, user space users who have some special
workloads can write personalized applications for better understanding
and optimizations of their workloads and systems.

===

Nevertheless, this commit is defining and implementing only basic access
check part without the overhead-accuracy handling core logic. The basic
access check is as below.

The output of DAMON says what memory regions are how frequently accessed
for a given duration. The resolution of the access frequency is
controlled by setting ``sampling interval`` and ``aggregation
interval``. In detail, DAMON checks access to each page per ``sampling
interval`` and aggregates the results. In other words, counts the
number of the accesses to each region. After each ``aggregation
interval`` passes, DAMON calls callback functions that previously
registered by users so that users can read the aggregated results and
then clears the results. This can be described in below simple
pseudo-code::

init()
while monitoring_on:
for page in monitoring_target:
if accessed(page):
nr_accesses[page] += 1
if time() % aggregation_interval == 0:
for callback in user_registered_callbacks:
callback(monitoring_target, nr_accesses)
for page in monitoring_target:
nr_accesses[page] = 0
if time() % update_interval == 0:
update()
sleep(sampling interval)

The target regions constructed at the beginning of the monitoring and
updated after each ``regions_update_interval``, because the target
regions could be dynamically changed (e.g., mmap() or memory hotplug).
The monitoring overhead of this mechanism will arbitrarily increase as
the size of the target workload grows.

The basic monitoring primitives for actual access check and dynamic
target regions construction aren't in the core part of DAMON. Instead,
it allows users to implement their own primitives that are optimized for
their use case and configure DAMON to use those. In other words, users
cannot use current version of DAMON without some additional works.

Following commits will implement the core mechanisms for the
overhead-accuracy control and default primitives implementations.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Leonard Foerster <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
include/linux/damon.h | 167 ++++++++++++++++++++++
mm/Kconfig | 2 +
mm/Makefile | 1 +
mm/damon/Kconfig | 15 ++
mm/damon/Makefile | 3 +
mm/damon/core.c | 318 ++++++++++++++++++++++++++++++++++++++++++
6 files changed, 506 insertions(+)
create mode 100644 include/linux/damon.h
create mode 100644 mm/damon/Kconfig
create mode 100644 mm/damon/Makefile
create mode 100644 mm/damon/core.c

diff --git a/include/linux/damon.h b/include/linux/damon.h
new file mode 100644
index 000000000000..2f652602b1ea
--- /dev/null
+++ b/include/linux/damon.h
@@ -0,0 +1,167 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DAMON api
+ *
+ * Author: SeongJae Park <[email protected]>
+ */
+
+#ifndef _DAMON_H_
+#define _DAMON_H_
+
+#include <linux/mutex.h>
+#include <linux/time64.h>
+#include <linux/types.h>
+
+struct damon_ctx;
+
+/**
+ * struct damon_primitive Monitoring primitives for given use cases.
+ *
+ * @init: Initialize primitive-internal data structures.
+ * @update: Update primitive-internal data structures.
+ * @prepare_access_checks: Prepare next access check of target regions.
+ * @check_accesses: Check the accesses to target regions.
+ * @reset_aggregated: Reset aggregated accesses monitoring results.
+ * @target_valid: Determine if the target is valid.
+ * @cleanup: Clean up the context.
+ *
+ * DAMON can be extended for various address spaces and usages. For this,
+ * users should register the low level primitives for their target address
+ * space and usecase via the &damon_ctx.primitive. Then, the monitoring thread
+ * (&damon_ctx.kdamond) calls @init and @prepare_access_checks before starting
+ * the monitoring, @update after each &damon_ctx.primitive_update_interval, and
+ * @check_accesses, @target_valid and @prepare_access_checks after each
+ * &damon_ctx.sample_interval. Finally, @reset_aggregated is called after each
+ * &damon_ctx.aggr_interval.
+ *
+ * @init should initialize primitive-internal data structures. For example,
+ * this could be used to construct proper monitoring target regions and link
+ * those to @damon_ctx.target.
+ * @update should update the primitive-internal data structures. For example,
+ * this could be used to update monitoring target regions for current status.
+ * @prepare_access_checks should manipulate the monitoring regions to be
+ * prepared for the next access check.
+ * @check_accesses should check the accesses to each region that made after the
+ * last preparation and update the number of observed accesses of each region.
+ * @reset_aggregated should reset the access monitoring results that aggregated
+ * by @check_accesses.
+ * @target_valid should check whether the target is still valid for the
+ * monitoring.
+ * @cleanup is called from @kdamond just before its termination.
+ */
+struct damon_primitive {
+ void (*init)(struct damon_ctx *context);
+ void (*update)(struct damon_ctx *context);
+ void (*prepare_access_checks)(struct damon_ctx *context);
+ void (*check_accesses)(struct damon_ctx *context);
+ void (*reset_aggregated)(struct damon_ctx *context);
+ bool (*target_valid)(void *target);
+ void (*cleanup)(struct damon_ctx *context);
+};
+
+/*
+ * struct damon_callback Monitoring events notification callbacks.
+ *
+ * @before_start: Called before starting the monitoring.
+ * @after_sampling: Called after each sampling.
+ * @after_aggregation: Called after each aggregation.
+ * @before_terminate: Called before terminating the monitoring.
+ * @private: User private data.
+ *
+ * The monitoring thread (&damon_ctx.kdamond) calls @before_start and
+ * @before_terminate just before starting and finishing the monitoring,
+ * respectively. Therefore, those are good places for installing and cleaning
+ * @private.
+ *
+ * The monitoring thread calls @after_sampling and @after_aggregation for each
+ * of the sampling intervals and aggregation intervals, respectively.
+ * Therefore, users can safely access the monitoring results without additional
+ * protection. For the reason, users are recommended to use these callback for
+ * the accesses to the results.
+ *
+ * If any callback returns non-zero, monitoring stops.
+ */
+struct damon_callback {
+ void *private;
+
+ int (*before_start)(struct damon_ctx *context);
+ int (*after_sampling)(struct damon_ctx *context);
+ int (*after_aggregation)(struct damon_ctx *context);
+ int (*before_terminate)(struct damon_ctx *context);
+};
+
+/**
+ * struct damon_ctx - Represents a context for each monitoring. This is the
+ * main interface that allows users to set the attributes and get the results
+ * of the monitoring.
+ *
+ * @sample_interval: The time between access samplings.
+ * @aggr_interval: The time between monitor results aggregations.
+ * @primitive_update_interval: The time between monitoring primitive updates.
+ *
+ * For each @sample_interval, DAMON checks whether each region is accessed or
+ * not. It aggregates and keeps the access information (number of accesses to
+ * each region) for @aggr_interval time. DAMON also checks whether the target
+ * memory regions need update (e.g., by ``mmap()`` calls from the application,
+ * in case of virtual memory monitoring) and applies the changes for each
+ * @primitive_update_interval. All time intervals are in micro-seconds.
+ * Please refer to &struct damon_primitive and &struct damon_callback for more
+ * detail.
+ *
+ * @kdamond: Kernel thread who does the monitoring.
+ * @kdamond_stop: Notifies whether kdamond should stop.
+ * @kdamond_lock: Mutex for the synchronizations with @kdamond.
+ *
+ * For each monitoring context, one kernel thread for the monitoring is
+ * created. The pointer to the thread is stored in @kdamond.
+ *
+ * Once started, the monitoring thread runs until explicitly required to be
+ * terminated or every monitoring target is invalid. The validity of the
+ * targets is checked via the &damon_primitive.target_valid of @primitive. The
+ * termination can also be explicitly requested by writing non-zero to
+ * @kdamond_stop. The thread sets @kdamond to NULL when it terminates.
+ * Therefore, users can know whether the monitoring is ongoing or terminated by
+ * reading @kdamond. Reads and writes to @kdamond and @kdamond_stop from
+ * outside of the monitoring thread must be protected by @kdamond_lock.
+ *
+ * Note that the monitoring thread protects only @kdamond and @kdamond_stop via
+ * @kdamond_lock. Accesses to other fields must be protected by themselves.
+ *
+ * @primitive: Set of monitoring primitives for given use cases.
+ * @callback: Set of callbacks for monitoring events notifications.
+ *
+ * @target: Pointer to the user-defined monitoring target.
+ */
+struct damon_ctx {
+ unsigned long sample_interval;
+ unsigned long aggr_interval;
+ unsigned long primitive_update_interval;
+
+/* private: internal use only */
+ struct timespec64 last_aggregation;
+ struct timespec64 last_primitive_update;
+
+/* public: */
+ struct task_struct *kdamond;
+ bool kdamond_stop;
+ struct mutex kdamond_lock;
+
+ struct damon_primitive primitive;
+ struct damon_callback callback;
+
+ void *target;
+};
+
+#ifdef CONFIG_DAMON
+
+struct damon_ctx *damon_new_ctx(void);
+void damon_destroy_ctx(struct damon_ctx *ctx);
+int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
+ unsigned long aggr_int, unsigned long primitive_upd_int);
+
+int damon_start(struct damon_ctx **ctxs, int nr_ctxs);
+int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
+
+#endif /* CONFIG_DAMON */
+
+#endif /* _DAMON_H */
diff --git a/mm/Kconfig b/mm/Kconfig
index 8f748010f7ea..44776162ae0d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -888,4 +888,6 @@ config IO_MAPPING
config SECRETMEM
def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED

+source "mm/damon/Kconfig"
+
endmenu
diff --git a/mm/Makefile b/mm/Makefile
index e3436741d539..709674b13497 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -128,3 +128,4 @@ obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
obj-$(CONFIG_IO_MAPPING) += io-mapping.o
obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
+obj-$(CONFIG_DAMON) += damon/
diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
new file mode 100644
index 000000000000..d00e99ac1a15
--- /dev/null
+++ b/mm/damon/Kconfig
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+menu "Data Access Monitoring"
+
+config DAMON
+ bool "DAMON: Data Access Monitoring Framework"
+ help
+ This builds a framework that allows kernel subsystems to monitor
+ access frequency of each memory region. The information can be useful
+ for performance-centric DRAM level memory management.
+
+ See https://damonitor.github.io/doc/html/latest-damon/index.html for
+ more information.
+
+endmenu
diff --git a/mm/damon/Makefile b/mm/damon/Makefile
new file mode 100644
index 000000000000..4fd2edb4becf
--- /dev/null
+++ b/mm/damon/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_DAMON) := core.o
diff --git a/mm/damon/core.c b/mm/damon/core.c
new file mode 100644
index 000000000000..693e51ebc05a
--- /dev/null
+++ b/mm/damon/core.c
@@ -0,0 +1,318 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Data Access Monitor
+ *
+ * Author: SeongJae Park <[email protected]>
+ */
+
+#define pr_fmt(fmt) "damon: " fmt
+
+#include <linux/damon.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/slab.h>
+
+static DEFINE_MUTEX(damon_lock);
+static int nr_running_ctxs;
+
+struct damon_ctx *damon_new_ctx(void)
+{
+ struct damon_ctx *ctx;
+
+ ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+ if (!ctx)
+ return NULL;
+
+ ctx->sample_interval = 5 * 1000;
+ ctx->aggr_interval = 100 * 1000;
+ ctx->primitive_update_interval = 1000 * 1000;
+
+ ktime_get_coarse_ts64(&ctx->last_aggregation);
+ ctx->last_primitive_update = ctx->last_aggregation;
+
+ mutex_init(&ctx->kdamond_lock);
+
+ ctx->target = NULL;
+
+ return ctx;
+}
+
+void damon_destroy_ctx(struct damon_ctx *ctx)
+{
+ if (ctx->primitive.cleanup)
+ ctx->primitive.cleanup(ctx);
+ kfree(ctx);
+}
+
+/**
+ * damon_set_attrs() - Set attributes for the monitoring.
+ * @ctx: monitoring context
+ * @sample_int: time interval between samplings
+ * @aggr_int: time interval between aggregations
+ * @primitive_upd_int: time interval between monitoring primitive updates
+ *
+ * This function should not be called while the kdamond is running.
+ * Every time interval is in micro-seconds.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
+ unsigned long aggr_int, unsigned long primitive_upd_int)
+{
+ ctx->sample_interval = sample_int;
+ ctx->aggr_interval = aggr_int;
+ ctx->primitive_update_interval = primitive_upd_int;
+
+ return 0;
+}
+
+static bool damon_kdamond_running(struct damon_ctx *ctx)
+{
+ bool running;
+
+ mutex_lock(&ctx->kdamond_lock);
+ running = ctx->kdamond != NULL;
+ mutex_unlock(&ctx->kdamond_lock);
+
+ return running;
+}
+
+static int kdamond_fn(void *data);
+
+/*
+ * __damon_start() - Starts monitoring with given context.
+ * @ctx: monitoring context
+ *
+ * This function should be called while damon_lock is hold.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+static int __damon_start(struct damon_ctx *ctx)
+{
+ int err = -EBUSY;
+
+ mutex_lock(&ctx->kdamond_lock);
+ if (!ctx->kdamond) {
+ err = 0;
+ ctx->kdamond_stop = false;
+ ctx->kdamond = kthread_create(kdamond_fn, ctx, "kdamond.%d",
+ nr_running_ctxs);
+ if (IS_ERR(ctx->kdamond))
+ err = PTR_ERR(ctx->kdamond);
+ else
+ wake_up_process(ctx->kdamond);
+ }
+ mutex_unlock(&ctx->kdamond_lock);
+
+ return err;
+}
+
+/**
+ * damon_start() - Starts the monitorings for a given group of contexts.
+ * @ctxs: an array of the pointers for contexts to start monitoring
+ * @nr_ctxs: size of @ctxs
+ *
+ * This function starts a group of monitoring threads for a group of monitoring
+ * contexts. One thread per each context is created and run in parallel. The
+ * caller should handle synchronization between the threads by itself. If a
+ * group of threads that created by other 'damon_start()' call is currently
+ * running, this function does nothing but returns -EBUSY.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int damon_start(struct damon_ctx **ctxs, int nr_ctxs)
+{
+ int i;
+ int err = 0;
+
+ mutex_lock(&damon_lock);
+ if (nr_running_ctxs) {
+ mutex_unlock(&damon_lock);
+ return -EBUSY;
+ }
+
+ for (i = 0; i < nr_ctxs; i++) {
+ err = __damon_start(ctxs[i]);
+ if (err)
+ break;
+ nr_running_ctxs++;
+ }
+ mutex_unlock(&damon_lock);
+
+ return err;
+}
+
+/*
+ * __damon_stop() - Stops monitoring of given context.
+ * @ctx: monitoring context
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+static int __damon_stop(struct damon_ctx *ctx)
+{
+ mutex_lock(&ctx->kdamond_lock);
+ if (ctx->kdamond) {
+ ctx->kdamond_stop = true;
+ mutex_unlock(&ctx->kdamond_lock);
+ while (damon_kdamond_running(ctx))
+ usleep_range(ctx->sample_interval,
+ ctx->sample_interval * 2);
+ return 0;
+ }
+ mutex_unlock(&ctx->kdamond_lock);
+
+ return -EPERM;
+}
+
+/**
+ * damon_stop() - Stops the monitorings for a given group of contexts.
+ * @ctxs: an array of the pointers for contexts to stop monitoring
+ * @nr_ctxs: size of @ctxs
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int damon_stop(struct damon_ctx **ctxs, int nr_ctxs)
+{
+ int i, err = 0;
+
+ for (i = 0; i < nr_ctxs; i++) {
+ /* nr_running_ctxs is decremented in kdamond_fn */
+ err = __damon_stop(ctxs[i]);
+ if (err)
+ return err;
+ }
+
+ return err;
+}
+
+/*
+ * damon_check_reset_time_interval() - Check if a time interval is elapsed.
+ * @baseline: the time to check whether the interval has elapsed since
+ * @interval: the time interval (microseconds)
+ *
+ * See whether the given time interval has passed since the given baseline
+ * time. If so, it also updates the baseline to current time for next check.
+ *
+ * Return: true if the time interval has passed, or false otherwise.
+ */
+static bool damon_check_reset_time_interval(struct timespec64 *baseline,
+ unsigned long interval)
+{
+ struct timespec64 now;
+
+ ktime_get_coarse_ts64(&now);
+ if ((timespec64_to_ns(&now) - timespec64_to_ns(baseline)) <
+ interval * 1000)
+ return false;
+ *baseline = now;
+ return true;
+}
+
+/*
+ * Check whether it is time to flush the aggregated information
+ */
+static bool kdamond_aggregate_interval_passed(struct damon_ctx *ctx)
+{
+ return damon_check_reset_time_interval(&ctx->last_aggregation,
+ ctx->aggr_interval);
+}
+
+/*
+ * Check whether it is time to check and apply the target monitoring regions
+ *
+ * Returns true if it is.
+ */
+static bool kdamond_need_update_primitive(struct damon_ctx *ctx)
+{
+ return damon_check_reset_time_interval(&ctx->last_primitive_update,
+ ctx->primitive_update_interval);
+}
+
+/*
+ * Check whether current monitoring should be stopped
+ *
+ * The monitoring is stopped when either the user requested to stop, or all
+ * monitoring targets are invalid.
+ *
+ * Returns true if need to stop current monitoring.
+ */
+static bool kdamond_need_stop(struct damon_ctx *ctx)
+{
+ bool stop;
+
+ mutex_lock(&ctx->kdamond_lock);
+ stop = ctx->kdamond_stop;
+ mutex_unlock(&ctx->kdamond_lock);
+ if (stop)
+ return true;
+
+ if (!ctx->primitive.target_valid)
+ return false;
+
+ return !ctx->primitive.target_valid(ctx->target);
+}
+
+static void set_kdamond_stop(struct damon_ctx *ctx)
+{
+ mutex_lock(&ctx->kdamond_lock);
+ ctx->kdamond_stop = true;
+ mutex_unlock(&ctx->kdamond_lock);
+}
+
+/*
+ * The monitoring daemon that runs as a kernel thread
+ */
+static int kdamond_fn(void *data)
+{
+ struct damon_ctx *ctx = (struct damon_ctx *)data;
+
+ pr_info("kdamond (%d) starts\n", ctx->kdamond->pid);
+
+ if (ctx->primitive.init)
+ ctx->primitive.init(ctx);
+ if (ctx->callback.before_start && ctx->callback.before_start(ctx))
+ set_kdamond_stop(ctx);
+
+ while (!kdamond_need_stop(ctx)) {
+ if (ctx->primitive.prepare_access_checks)
+ ctx->primitive.prepare_access_checks(ctx);
+ if (ctx->callback.after_sampling &&
+ ctx->callback.after_sampling(ctx))
+ set_kdamond_stop(ctx);
+
+ usleep_range(ctx->sample_interval, ctx->sample_interval + 1);
+
+ if (ctx->primitive.check_accesses)
+ ctx->primitive.check_accesses(ctx);
+
+ if (kdamond_aggregate_interval_passed(ctx)) {
+ if (ctx->callback.after_aggregation &&
+ ctx->callback.after_aggregation(ctx))
+ set_kdamond_stop(ctx);
+ if (ctx->primitive.reset_aggregated)
+ ctx->primitive.reset_aggregated(ctx);
+ }
+
+ if (kdamond_need_update_primitive(ctx)) {
+ if (ctx->primitive.update)
+ ctx->primitive.update(ctx);
+ }
+ }
+
+ if (ctx->callback.before_terminate &&
+ ctx->callback.before_terminate(ctx))
+ set_kdamond_stop(ctx);
+ if (ctx->primitive.cleanup)
+ ctx->primitive.cleanup(ctx);
+
+ pr_debug("kdamond (%d) finishes\n", ctx->kdamond->pid);
+ mutex_lock(&ctx->kdamond_lock);
+ ctx->kdamond = NULL;
+ mutex_unlock(&ctx->kdamond_lock);
+
+ mutex_lock(&damon_lock);
+ nr_running_ctxs--;
+ mutex_unlock(&damon_lock);
+
+ do_exit(0);
+}
--
2.17.1

2021-06-21 08:32:45

by SeongJae Park

Subject: [PATCH v31 04/13] mm/idle_page_tracking: Make PG_idle reusable

From: SeongJae Park <[email protected]>

PG_idle and PG_young allow the two PTE Accessed bit users, Idle Page
Tracking and the reclaim logic concurrently work while not interfering
with each other. That is, when they need to clear the Accessed bit,
they set PG_young to represent the previous state of the bit,
respectively. And when they need to read the bit, if the bit is
cleared, they further read the PG_young to know whether the other has
cleared the bit meanwhile or not.

For yet another user of the PTE Accessed bit, we could add another page
flag, or extend the mechanism to use the flags. For the DAMON usecase,
however, we don't need to do that just yet. IDLE_PAGE_TRACKING and
DAMON are mutually exclusive, so there's only ever going to be one user
of the current set of flags.

In this commit, we split out the CONFIG options to allow for the use of
PG_young and PG_idle outside of idle page tracking.

In the next commit, DAMON's reference implementation of the virtual
memory address space monitoring primitives will use it.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
include/linux/page-flags.h | 4 ++--
include/linux/page_ext.h | 2 +-
include/linux/page_idle.h | 6 +++---
include/trace/events/mmflags.h | 2 +-
mm/Kconfig | 8 ++++++++
mm/page_ext.c | 12 +++++++++++-
mm/page_idle.c | 10 ----------
7 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 5922031ffab6..5621d628914d 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -131,7 +131,7 @@ enum pageflags {
#ifdef CONFIG_MEMORY_FAILURE
PG_hwpoison, /* hardware poisoned page. Don't touch */
#endif
-#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
+#if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
PG_young,
PG_idle,
#endif
@@ -439,7 +439,7 @@ PAGEFLAG_FALSE(HWPoison)
#define __PG_HWPOISON 0
#endif

-#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
+#if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
TESTPAGEFLAG(Young, young, PF_ANY)
SETPAGEFLAG(Young, young, PF_ANY)
TESTCLEARFLAG(Young, young, PF_ANY)
diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index aff81ba31bd8..fabb2e1e087f 100644
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -19,7 +19,7 @@ struct page_ext_operations {
enum page_ext_flags {
PAGE_EXT_OWNER,
PAGE_EXT_OWNER_ALLOCATED,
-#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
+#if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT)
PAGE_EXT_YOUNG,
PAGE_EXT_IDLE,
#endif
diff --git a/include/linux/page_idle.h b/include/linux/page_idle.h
index 1e894d34bdce..d8a6aecf99cb 100644
--- a/include/linux/page_idle.h
+++ b/include/linux/page_idle.h
@@ -6,7 +6,7 @@
#include <linux/page-flags.h>
#include <linux/page_ext.h>

-#ifdef CONFIG_IDLE_PAGE_TRACKING
+#ifdef CONFIG_PAGE_IDLE_FLAG

#ifdef CONFIG_64BIT
static inline bool page_is_young(struct page *page)
@@ -106,7 +106,7 @@ static inline void clear_page_idle(struct page *page)
}
#endif /* CONFIG_64BIT */

-#else /* !CONFIG_IDLE_PAGE_TRACKING */
+#else /* !CONFIG_PAGE_IDLE_FLAG */

static inline bool page_is_young(struct page *page)
{
@@ -135,6 +135,6 @@ static inline void clear_page_idle(struct page *page)
{
}

-#endif /* CONFIG_IDLE_PAGE_TRACKING */
+#endif /* CONFIG_PAGE_IDLE_FLAG */

#endif /* _LINUX_MM_PAGE_IDLE_H */
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index 390270e00a1d..d428f0137c49 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -73,7 +73,7 @@
#define IF_HAVE_PG_HWPOISON(flag,string)
#endif

-#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
+#if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
#define IF_HAVE_PG_IDLE(flag,string) ,{1UL << flag, string}
#else
#define IF_HAVE_PG_IDLE(flag,string)
diff --git a/mm/Kconfig b/mm/Kconfig
index 44776162ae0d..88fb55b8b6d2 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -741,10 +741,18 @@ config DEFERRED_STRUCT_PAGE_INIT
lifetime of the system until these kthreads finish the
initialisation.

+config PAGE_IDLE_FLAG
+ bool "Add PG_idle and PG_young flags"
+ help
+ This feature adds PG_idle and PG_young flags in 'struct page'. PTE
+ Accessed bit writers can set the state of the bit in the flags to let
+ other PTE Accessed bit readers don't disturbed.
+
config IDLE_PAGE_TRACKING
bool "Enable idle page tracking"
depends on SYSFS && MMU && BROKEN
select PAGE_EXTENSION if !64BIT
+ select PAGE_IDLE_FLAG
help
This feature allows to estimate the amount of user pages that have
not been touched during a given period of time. This information can
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 293b2685fc48..dfb91653d359 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -58,11 +58,21 @@
* can utilize this callback to initialize the state of it correctly.
*/

+#if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT)
+static bool need_page_idle(void)
+{
+ return true;
+}
+struct page_ext_operations page_idle_ops = {
+ .need = need_page_idle,
+};
+#endif
+
static struct page_ext_operations *page_ext_ops[] = {
#ifdef CONFIG_PAGE_OWNER
&page_owner_ops,
#endif
-#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
+#if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT)
&page_idle_ops,
#endif
};
diff --git a/mm/page_idle.c b/mm/page_idle.c
index 64e5344a992c..edead6a8a5f9 100644
--- a/mm/page_idle.c
+++ b/mm/page_idle.c
@@ -207,16 +207,6 @@ static const struct attribute_group page_idle_attr_group = {
.name = "page_idle",
};

-#ifndef CONFIG_64BIT
-static bool need_page_idle(void)
-{
- return true;
-}
-struct page_ext_operations page_idle_ops = {
- .need = need_page_idle,
-};
-#endif
-
static int __init page_idle_init(void)
{
int err;
--
2.17.1

2021-06-21 08:32:54

by SeongJae Park

Subject: [PATCH v31 06/13] mm/damon: Add a tracepoint

From: SeongJae Park <[email protected]>

This commit adds a tracepoint for DAMON. It traces the monitoring
results of each region for each aggregation interval. Using this, DAMON
can easily integrated with tracepoints supporting tools such as perf.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Leonard Foerster <[email protected]>
Reviewed-by: Steven Rostedt (VMware) <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
include/trace/events/damon.h | 43 ++++++++++++++++++++++++++++++++++++
mm/damon/core.c | 7 +++++-
2 files changed, 49 insertions(+), 1 deletion(-)
create mode 100644 include/trace/events/damon.h

diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
new file mode 100644
index 000000000000..2f422f4f1fb9
--- /dev/null
+++ b/include/trace/events/damon.h
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM damon
+
+#if !defined(_TRACE_DAMON_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_DAMON_H
+
+#include <linux/damon.h>
+#include <linux/types.h>
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(damon_aggregated,
+
+ TP_PROTO(struct damon_target *t, struct damon_region *r,
+ unsigned int nr_regions),
+
+ TP_ARGS(t, r, nr_regions),
+
+ TP_STRUCT__entry(
+ __field(unsigned long, target_id)
+ __field(unsigned int, nr_regions)
+ __field(unsigned long, start)
+ __field(unsigned long, end)
+ __field(unsigned int, nr_accesses)
+ ),
+
+ TP_fast_assign(
+ __entry->target_id = t->id;
+ __entry->nr_regions = nr_regions;
+ __entry->start = r->ar.start;
+ __entry->end = r->ar.end;
+ __entry->nr_accesses = r->nr_accesses;
+ ),
+
+ TP_printk("target_id=%lu nr_regions=%u %lu-%lu: %u",
+ __entry->target_id, __entry->nr_regions,
+ __entry->start, __entry->end, __entry->nr_accesses)
+);
+
+#endif /* _TRACE_DAMON_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/mm/damon/core.c b/mm/damon/core.c
index b36b6bdd94e2..912112662d0c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -13,6 +13,9 @@
#include <linux/random.h>
#include <linux/slab.h>

+#define CREATE_TRACE_POINTS
+#include <trace/events/damon.h>
+
/* Get a random number in [l, r) */
#define damon_rand(l, r) (l + prandom_u32_max(r - l))

@@ -388,8 +391,10 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
damon_for_each_target(t, c) {
struct damon_region *r;

- damon_for_each_region(r, t)
+ damon_for_each_region(r, t) {
+ trace_damon_aggregated(t, r, damon_nr_regions(t));
r->nr_accesses = 0;
+ }
}
}

--
2.17.1

2021-06-21 08:33:00

by SeongJae Park

Subject: [PATCH v31 07/13] mm/damon: Implement a debugfs-based user space interface

From: SeongJae Park <[email protected]>

DAMON is designed to be used by kernel space code such as the memory
management subsystems, and therefore it provides only kernel space API.
That said, letting the user space control DAMON could provide some
benefits to them. For example, it will allow user space to analyze
their specific workloads and make their own special optimizations.

For such cases, this commit implements a simple DAMON application kernel
module, namely 'damon-dbgfs', which merely wraps the DAMON api and
exports those to the user space via the debugfs.

'damon-dbgfs' exports three files, ``attrs``, ``target_ids``, and
``monitor_on`` under its debugfs directory, ``<debugfs>/damon/``.

Attributes
----------

Users can read and write the ``sampling interval``, ``aggregation
interval``, ``regions update interval``, and min/max number of
monitoring target regions by reading from and writing to the ``attrs``
file. For example, below commands set those values to 5 ms, 100 ms,
1,000 ms, 10, 1000 and check it again::

# cd <debugfs>/damon
# echo 5000 100000 1000000 10 1000 > attrs
# cat attrs
5000 100000 1000000 10 1000

Target IDs
----------

Some types of address spaces supports multiple monitoring target. For
example, the virtual memory address spaces monitoring can have multiple
processes as the monitoring targets. Users can set the targets by
writing relevant id values of the targets to, and get the ids of the
current targets by reading from the ``target_ids`` file. In case of the
virtual address spaces monitoring, the values should be pids of the
monitoring target processes. For example, below commands set processes
having pids 42 and 4242 as the monitoring targets and check it again::

# cd <debugfs>/damon
# echo 42 4242 > target_ids
# cat target_ids
42 4242

Note that setting the target ids doesn't start the monitoring.

Turning On/Off
--------------

Setting the files as described above doesn't incur effect unless you
explicitly start the monitoring. You can start, stop, and check the
current status of the monitoring by writing to and reading from the
``monitor_on`` file. Writing ``on`` to the file starts the monitoring
of the targets with the attributes. Writing ``off`` to the file stops
those. DAMON also stops if every targets are invalidated (in case of
the virtual memory monitoring, target processes are invalidated when
terminated). Below example commands turn on, off, and check the status
of DAMON::

# cd <debugfs>/damon
# echo on > monitor_on
# echo off > monitor_on
# cat monitor_on
off

Please note that you cannot write to the above-mentioned debugfs files
while the monitoring is turned on. If you write to the files while
DAMON is running, an error code such as ``-EBUSY`` will be returned.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Leonard Foerster <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
include/linux/damon.h | 3 +
mm/damon/Kconfig | 9 +
mm/damon/Makefile | 1 +
mm/damon/core.c | 47 +++++
mm/damon/dbgfs.c | 386 ++++++++++++++++++++++++++++++++++++++++++
5 files changed, 446 insertions(+)
create mode 100644 mm/damon/dbgfs.c

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 72cf5ebd35fe..b17e808a9cae 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -237,9 +237,12 @@ unsigned int damon_nr_regions(struct damon_target *t);

struct damon_ctx *damon_new_ctx(void);
void damon_destroy_ctx(struct damon_ctx *ctx);
+int damon_set_targets(struct damon_ctx *ctx,
+ unsigned long *ids, ssize_t nr_ids);
int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
unsigned long aggr_int, unsigned long primitive_upd_int,
unsigned long min_nr_reg, unsigned long max_nr_reg);
+int damon_nr_running_ctxs(void);

int damon_start(struct damon_ctx **ctxs, int nr_ctxs);
int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
index 8ae080c52950..72f1683ba0ee 100644
--- a/mm/damon/Kconfig
+++ b/mm/damon/Kconfig
@@ -21,4 +21,13 @@ config DAMON_VADDR
This builds the default data access monitoring primitives for DAMON
that works for virtual address spaces.

+config DAMON_DBGFS
+ bool "DAMON debugfs interface"
+ depends on DAMON_VADDR && DEBUG_FS
+ help
+ This builds the debugfs interface for DAMON. The user space admins
+ can use the interface for arbitrary data access monitoring.
+
+ If unsure, say N.
+
endmenu
diff --git a/mm/damon/Makefile b/mm/damon/Makefile
index 6ebbd08aed67..fed4be3bace3 100644
--- a/mm/damon/Makefile
+++ b/mm/damon/Makefile
@@ -2,3 +2,4 @@

obj-$(CONFIG_DAMON) := core.o
obj-$(CONFIG_DAMON_VADDR) += vaddr.o
+obj-$(CONFIG_DAMON_DBGFS) += dbgfs.o
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 912112662d0c..cad2b4cee39d 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -172,6 +172,39 @@ void damon_destroy_ctx(struct damon_ctx *ctx)
kfree(ctx);
}

+/**
+ * damon_set_targets() - Set monitoring targets.
+ * @ctx: monitoring context
+ * @ids: array of target ids
+ * @nr_ids: number of entries in @ids
+ *
+ * This function should not be called while the kdamond is running.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int damon_set_targets(struct damon_ctx *ctx,
+ unsigned long *ids, ssize_t nr_ids)
+{
+ ssize_t i;
+ struct damon_target *t, *next;
+
+ damon_destroy_targets(ctx);
+
+ for (i = 0; i < nr_ids; i++) {
+ t = damon_new_target(ids[i]);
+ if (!t) {
+ pr_err("Failed to alloc damon_target\n");
+ /* The caller should do cleanup of the ids itself */
+ damon_for_each_target_safe(t, next, ctx)
+ damon_destroy_target(t);
+ return -ENOMEM;
+ }
+ damon_add_target(ctx, t);
+ }
+
+ return 0;
+}
+
/**
* damon_set_attrs() - Set attributes for the monitoring.
* @ctx: monitoring context
@@ -210,6 +243,20 @@ int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
return 0;
}

+/**
+ * damon_nr_running_ctxs() - Return number of currently running contexts.
+ */
+int damon_nr_running_ctxs(void)
+{
+ int nr_ctxs;
+
+ mutex_lock(&damon_lock);
+ nr_ctxs = nr_running_ctxs;
+ mutex_unlock(&damon_lock);
+
+ return nr_ctxs;
+}
+
/* Returns the size upper limit for each monitoring region */
static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
{
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
new file mode 100644
index 000000000000..c4a4a6f1dc79
--- /dev/null
+++ b/mm/damon/dbgfs.c
@@ -0,0 +1,386 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DAMON Debugfs Interface
+ *
+ * Author: SeongJae Park <[email protected]>
+ */
+
+#define pr_fmt(fmt) "damon-dbgfs: " fmt
+
+#include <linux/damon.h>
+#include <linux/debugfs.h>
+#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/page_idle.h>
+#include <linux/slab.h>
+
+static struct damon_ctx **dbgfs_ctxs;
+static int dbgfs_nr_ctxs;
+static struct dentry **dbgfs_dirs;
+
+/*
+ * Returns non-empty string on success, negative error code otherwise.
+ */
+static char *user_input_str(const char __user *buf, size_t count, loff_t *ppos)
+{
+ char *kbuf;
+ ssize_t ret;
+
+ /* We do not accept continuous write */
+ if (*ppos)
+ return ERR_PTR(-EINVAL);
+
+ kbuf = kmalloc(count + 1, GFP_KERNEL);
+ if (!kbuf)
+ return ERR_PTR(-ENOMEM);
+
+ ret = simple_write_to_buffer(kbuf, count + 1, ppos, buf, count);
+ if (ret != count) {
+ kfree(kbuf);
+ return ERR_PTR(-EIO);
+ }
+ kbuf[ret] = '\0';
+
+ return kbuf;
+}
+
+static ssize_t dbgfs_attrs_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = file->private_data;
+ char kbuf[128];
+ int ret;
+
+ mutex_lock(&ctx->kdamond_lock);
+ ret = scnprintf(kbuf, ARRAY_SIZE(kbuf), "%lu %lu %lu %lu %lu\n",
+ ctx->sample_interval, ctx->aggr_interval,
+ ctx->primitive_update_interval, ctx->min_nr_regions,
+ ctx->max_nr_regions);
+ mutex_unlock(&ctx->kdamond_lock);
+
+ return simple_read_from_buffer(buf, count, ppos, kbuf, ret);
+}
+
+static ssize_t dbgfs_attrs_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = file->private_data;
+ unsigned long s, a, r, minr, maxr;
+ char *kbuf;
+ ssize_t ret = count;
+ int err;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ if (sscanf(kbuf, "%lu %lu %lu %lu %lu",
+ &s, &a, &r, &minr, &maxr) != 5) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ mutex_lock(&ctx->kdamond_lock);
+ if (ctx->kdamond) {
+ ret = -EBUSY;
+ goto unlock_out;
+ }
+
+ err = damon_set_attrs(ctx, s, a, r, minr, maxr);
+ if (err)
+ ret = err;
+unlock_out:
+ mutex_unlock(&ctx->kdamond_lock);
+out:
+ kfree(kbuf);
+ return ret;
+}
+
+#define targetid_is_pid(ctx) \
+ (ctx->primitive.target_valid == damon_va_target_valid)
+
+static ssize_t sprint_target_ids(struct damon_ctx *ctx, char *buf, ssize_t len)
+{
+ struct damon_target *t;
+ unsigned long id;
+ int written = 0;
+ int rc;
+
+ damon_for_each_target(t, ctx) {
+ id = t->id;
+ if (targetid_is_pid(ctx))
+ /* Show pid numbers to debugfs users */
+ id = (unsigned long)pid_vnr((struct pid *)id);
+
+ rc = scnprintf(&buf[written], len - written, "%lu ", id);
+ if (!rc)
+ return -ENOMEM;
+ written += rc;
+ }
+ if (written)
+ written -= 1;
+ written += scnprintf(&buf[written], len - written, "\n");
+ return written;
+}
+
+static ssize_t dbgfs_target_ids_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = file->private_data;
+ ssize_t len;
+ char ids_buf[320];
+
+ mutex_lock(&ctx->kdamond_lock);
+ len = sprint_target_ids(ctx, ids_buf, 320);
+ mutex_unlock(&ctx->kdamond_lock);
+ if (len < 0)
+ return len;
+
+ return simple_read_from_buffer(buf, count, ppos, ids_buf, len);
+}
+
+/*
+ * Converts a string into an array of unsigned long integers
+ *
+ * Returns an array of unsigned long integers if the conversion success, or
+ * NULL otherwise.
+ */
+static unsigned long *str_to_target_ids(const char *str, ssize_t len,
+ ssize_t *nr_ids)
+{
+ unsigned long *ids;
+ const int max_nr_ids = 32;
+ unsigned long id;
+ int pos = 0, parsed, ret;
+
+ *nr_ids = 0;
+ ids = kmalloc_array(max_nr_ids, sizeof(id), GFP_KERNEL);
+ if (!ids)
+ return NULL;
+ while (*nr_ids < max_nr_ids && pos < len) {
+ ret = sscanf(&str[pos], "%lu%n", &id, &parsed);
+ pos += parsed;
+ if (ret != 1)
+ break;
+ ids[*nr_ids] = id;
+ *nr_ids += 1;
+ }
+
+ return ids;
+}
+
+static void dbgfs_put_pids(unsigned long *ids, int nr_ids)
+{
+ int i;
+
+ for (i = 0; i < nr_ids; i++)
+ put_pid((struct pid *)ids[i]);
+}
+
+static ssize_t dbgfs_target_ids_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = file->private_data;
+ char *kbuf, *nrs;
+ unsigned long *targets;
+ ssize_t nr_targets;
+ ssize_t ret = count;
+ int i;
+ int err;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ nrs = kbuf;
+
+ targets = str_to_target_ids(nrs, ret, &nr_targets);
+ if (!targets) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ if (targetid_is_pid(ctx)) {
+ for (i = 0; i < nr_targets; i++) {
+ targets[i] = (unsigned long)find_get_pid(
+ (int)targets[i]);
+ if (!targets[i]) {
+ dbgfs_put_pids(targets, i);
+ ret = -EINVAL;
+ goto free_targets_out;
+ }
+ }
+ }
+
+ mutex_lock(&ctx->kdamond_lock);
+ if (ctx->kdamond) {
+ if (targetid_is_pid(ctx))
+ dbgfs_put_pids(targets, nr_targets);
+ ret = -EBUSY;
+ goto unlock_out;
+ }
+
+ err = damon_set_targets(ctx, targets, nr_targets);
+ if (err) {
+ if (targetid_is_pid(ctx))
+ dbgfs_put_pids(targets, nr_targets);
+ ret = err;
+ }
+
+unlock_out:
+ mutex_unlock(&ctx->kdamond_lock);
+free_targets_out:
+ kfree(targets);
+out:
+ kfree(kbuf);
+ return ret;
+}
+
+static int damon_dbgfs_open(struct inode *inode, struct file *file)
+{
+ file->private_data = inode->i_private;
+
+ return nonseekable_open(inode, file);
+}
+
+static const struct file_operations attrs_fops = {
+ .owner = THIS_MODULE,
+ .open = damon_dbgfs_open,
+ .read = dbgfs_attrs_read,
+ .write = dbgfs_attrs_write,
+};
+
+static const struct file_operations target_ids_fops = {
+ .owner = THIS_MODULE,
+ .open = damon_dbgfs_open,
+ .read = dbgfs_target_ids_read,
+ .write = dbgfs_target_ids_write,
+};
+
+static void dbgfs_fill_ctx_dir(struct dentry *dir, struct damon_ctx *ctx)
+{
+ const char * const file_names[] = {"attrs", "target_ids"};
+ const struct file_operations *fops[] = {&attrs_fops, &target_ids_fops};
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(file_names); i++)
+ debugfs_create_file(file_names[i], 0600, dir, ctx, fops[i]);
+}
+
+static struct damon_ctx *dbgfs_new_ctx(void)
+{
+ struct damon_ctx *ctx;
+
+ ctx = damon_new_ctx();
+ if (!ctx)
+ return NULL;
+
+ damon_va_set_primitives(ctx);
+ return ctx;
+}
+
+static ssize_t dbgfs_monitor_on_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ char monitor_on_buf[5];
+ bool monitor_on = damon_nr_running_ctxs() != 0;
+ int len;
+
+ len = scnprintf(monitor_on_buf, 5, monitor_on ? "on\n" : "off\n");
+
+ return simple_read_from_buffer(buf, count, ppos, monitor_on_buf, len);
+}
+
+static ssize_t dbgfs_monitor_on_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ ssize_t ret = count;
+ char *kbuf;
+ int err;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ /* Remove white space */
+ if (sscanf(kbuf, "%s", kbuf) != 1) {
+ kfree(kbuf);
+ return -EINVAL;
+ }
+
+ if (!strncmp(kbuf, "on", count))
+ err = damon_start(dbgfs_ctxs, dbgfs_nr_ctxs);
+ else if (!strncmp(kbuf, "off", count))
+ err = damon_stop(dbgfs_ctxs, dbgfs_nr_ctxs);
+ else
+ err = -EINVAL;
+
+ if (err)
+ ret = err;
+ kfree(kbuf);
+ return ret;
+}
+
+static const struct file_operations monitor_on_fops = {
+ .owner = THIS_MODULE,
+ .read = dbgfs_monitor_on_read,
+ .write = dbgfs_monitor_on_write,
+};
+
+static int __init __damon_dbgfs_init(void)
+{
+ struct dentry *dbgfs_root;
+ const char * const file_names[] = {"monitor_on"};
+ const struct file_operations *fops[] = {&monitor_on_fops};
+ int i;
+
+ dbgfs_root = debugfs_create_dir("damon", NULL);
+
+ for (i = 0; i < ARRAY_SIZE(file_names); i++)
+ debugfs_create_file(file_names[i], 0600, dbgfs_root, NULL,
+ fops[i]);
+ dbgfs_fill_ctx_dir(dbgfs_root, dbgfs_ctxs[0]);
+
+ dbgfs_dirs = kmalloc_array(1, sizeof(dbgfs_root), GFP_KERNEL);
+ if (!dbgfs_dirs) {
+ debugfs_remove(dbgfs_root);
+ return -ENOMEM;
+ }
+ dbgfs_dirs[0] = dbgfs_root;
+
+ return 0;
+}
+
+/*
+ * Functions for the initialization
+ */
+
+static int __init damon_dbgfs_init(void)
+{
+ int rc;
+
+ dbgfs_ctxs = kmalloc(sizeof(*dbgfs_ctxs), GFP_KERNEL);
+ if (!dbgfs_ctxs) {
+ pr_err("%s: dbgfs ctxs alloc failed\n", __func__);
+ return -ENOMEM;
+ }
+ dbgfs_ctxs[0] = dbgfs_new_ctx();
+ if (!dbgfs_ctxs[0]) {
+ kfree(dbgfs_ctxs);
+ pr_err("%s: dbgfs ctx alloc failed\n", __func__);
+ return -ENOMEM;
+ }
+ dbgfs_nr_ctxs = 1;
+
+ rc = __damon_dbgfs_init();
+ if (rc) {
+ kfree(dbgfs_ctxs[0]);
+ kfree(dbgfs_ctxs);
+ pr_err("%s: dbgfs init failed\n", __func__);
+ }
+
+ return rc;
+}
+
+module_init(damon_dbgfs_init);
--
2.17.1

2021-06-21 08:33:04

by SeongJae Park

Subject: [PATCH v31 08/13] mm/damon/dbgfs: Export kdamond pid to the user space

From: SeongJae Park <[email protected]>

For CPU usage accounting, knowing pid of the monitoring thread could be
helpful. For example, users could use cpuaccount cgroups with the pid.

This commit therefore exports the pid of currently running monitoring
thread to the user space via 'kdamond_pid' file in the debugfs
directory.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
mm/damon/dbgfs.c | 38 ++++++++++++++++++++++++++++++++++++--
1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index c4a4a6f1dc79..524362f8c628 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -237,6 +237,32 @@ static ssize_t dbgfs_target_ids_write(struct file *file,
return ret;
}

+static ssize_t dbgfs_kdamond_pid_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = file->private_data;
+ char *kbuf;
+ ssize_t len;
+
+ kbuf = kmalloc(count, GFP_KERNEL);
+ if (!kbuf)
+ return -ENOMEM;
+
+ mutex_lock(&ctx->kdamond_lock);
+ if (ctx->kdamond)
+ len = scnprintf(kbuf, count, "%d\n", ctx->kdamond->pid);
+ else
+ len = scnprintf(kbuf, count, "none\n");
+ mutex_unlock(&ctx->kdamond_lock);
+ if (!len)
+ goto out;
+ len = simple_read_from_buffer(buf, count, ppos, kbuf, len);
+
+out:
+ kfree(kbuf);
+ return len;
+}
+
static int damon_dbgfs_open(struct inode *inode, struct file *file)
{
file->private_data = inode->i_private;
@@ -258,10 +284,18 @@ static const struct file_operations target_ids_fops = {
.write = dbgfs_target_ids_write,
};

+static const struct file_operations kdamond_pid_fops = {
+ .owner = THIS_MODULE,
+ .open = damon_dbgfs_open,
+ .read = dbgfs_kdamond_pid_read,
+};
+
static void dbgfs_fill_ctx_dir(struct dentry *dir, struct damon_ctx *ctx)
{
- const char * const file_names[] = {"attrs", "target_ids"};
- const struct file_operations *fops[] = {&attrs_fops, &target_ids_fops};
+ const char * const file_names[] = {"attrs", "target_ids",
+ "kdamond_pid"};
+ const struct file_operations *fops[] = {&attrs_fops, &target_ids_fops,
+ &kdamond_pid_fops};
int i;

for (i = 0; i < ARRAY_SIZE(file_names); i++)
--
2.17.1

2021-06-21 08:33:17

by SeongJae Park

Subject: [PATCH v31 11/13] mm/damon: Add kunit tests

From: SeongJae Park <[email protected]>

This commit adds kunit based unit tests for the core and the virtual
address spaces monitoring primitives of DAMON.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Brendan Higgins <[email protected]>
---
mm/damon/Kconfig | 36 +++++
mm/damon/core-test.h | 253 ++++++++++++++++++++++++++++++++
mm/damon/core.c | 7 +
mm/damon/dbgfs-test.h | 126 ++++++++++++++++
mm/damon/dbgfs.c | 2 +
mm/damon/vaddr-test.h | 328 ++++++++++++++++++++++++++++++++++++++++++
mm/damon/vaddr.c | 7 +
7 files changed, 759 insertions(+)
create mode 100644 mm/damon/core-test.h
create mode 100644 mm/damon/dbgfs-test.h
create mode 100644 mm/damon/vaddr-test.h

diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
index 72f1683ba0ee..455995152697 100644
--- a/mm/damon/Kconfig
+++ b/mm/damon/Kconfig
@@ -12,6 +12,18 @@ config DAMON
See https://damonitor.github.io/doc/html/latest-damon/index.html for
more information.

+config DAMON_KUNIT_TEST
+ bool "Test for damon" if !KUNIT_ALL_TESTS
+ depends on DAMON && KUNIT=y
+ default KUNIT_ALL_TESTS
+ help
+ This builds the DAMON Kunit test suite.
+
+ For more information on KUnit and unit tests in general, please refer
+ to the KUnit documentation.
+
+ If unsure, say N.
+
config DAMON_VADDR
bool "Data access monitoring primitives for virtual address spaces"
depends on DAMON && MMU
@@ -21,6 +33,18 @@ config DAMON_VADDR
This builds the default data access monitoring primitives for DAMON
that works for virtual address spaces.

+config DAMON_VADDR_KUNIT_TEST
+ bool "Test for DAMON primitives" if !KUNIT_ALL_TESTS
+ depends on DAMON_VADDR && KUNIT=y
+ default KUNIT_ALL_TESTS
+ help
+ This builds the DAMON virtual addresses primitives Kunit test suite.
+
+ For more information on KUnit and unit tests in general, please refer
+ to the KUnit documentation.
+
+ If unsure, say N.
+
config DAMON_DBGFS
bool "DAMON debugfs interface"
depends on DAMON_VADDR && DEBUG_FS
@@ -30,4 +54,16 @@ config DAMON_DBGFS

If unsure, say N.

+config DAMON_DBGFS_KUNIT_TEST
+ bool "Test for damon debugfs interface" if !KUNIT_ALL_TESTS
+ depends on DAMON_DBGFS && KUNIT=y
+ default KUNIT_ALL_TESTS
+ help
+ This builds the DAMON debugfs interface Kunit test suite.
+
+ For more information on KUnit and unit tests in general, please refer
+ to the KUnit documentation.
+
+ If unsure, say N.
+
endmenu
diff --git a/mm/damon/core-test.h b/mm/damon/core-test.h
new file mode 100644
index 000000000000..b815dfbfb5fd
--- /dev/null
+++ b/mm/damon/core-test.h
@@ -0,0 +1,253 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Data Access Monitor Unit Tests
+ *
+ * Copyright 2019 Amazon.com, Inc. or its affiliates. All rights reserved.
+ *
+ * Author: SeongJae Park <[email protected]>
+ */
+
+#ifdef CONFIG_DAMON_KUNIT_TEST
+
+#ifndef _DAMON_CORE_TEST_H
+#define _DAMON_CORE_TEST_H
+
+#include <kunit/test.h>
+
+static void damon_test_regions(struct kunit *test)
+{
+ struct damon_region *r;
+ struct damon_target *t;
+
+ r = damon_new_region(1, 2);
+ KUNIT_EXPECT_EQ(test, 1ul, r->ar.start);
+ KUNIT_EXPECT_EQ(test, 2ul, r->ar.end);
+ KUNIT_EXPECT_EQ(test, 0u, r->nr_accesses);
+
+ t = damon_new_target(42);
+ KUNIT_EXPECT_EQ(test, 0u, damon_nr_regions(t));
+
+ damon_add_region(r, t);
+ KUNIT_EXPECT_EQ(test, 1u, damon_nr_regions(t));
+
+ damon_del_region(r);
+ KUNIT_EXPECT_EQ(test, 0u, damon_nr_regions(t));
+
+ damon_free_target(t);
+}
+
+static unsigned int nr_damon_targets(struct damon_ctx *ctx)
+{
+ struct damon_target *t;
+ unsigned int nr_targets = 0;
+
+ damon_for_each_target(t, ctx)
+ nr_targets++;
+
+ return nr_targets;
+}
+
+static void damon_test_target(struct kunit *test)
+{
+ struct damon_ctx *c = damon_new_ctx();
+ struct damon_target *t;
+
+ t = damon_new_target(42);
+ KUNIT_EXPECT_EQ(test, 42ul, t->id);
+ KUNIT_EXPECT_EQ(test, 0u, nr_damon_targets(c));
+
+ damon_add_target(c, t);
+ KUNIT_EXPECT_EQ(test, 1u, nr_damon_targets(c));
+
+ damon_destroy_target(t);
+ KUNIT_EXPECT_EQ(test, 0u, nr_damon_targets(c));
+
+ damon_destroy_ctx(c);
+}
+
+/*
+ * Test kdamond_reset_aggregated()
+ *
+ * DAMON checks access to each region and aggregates this information as the
+ * access frequency of each region. In detail, it increases '->nr_accesses' of
+ * regions that an access has confirmed. 'kdamond_reset_aggregated()' flushes
+ * the aggregated information ('->nr_accesses' of each regions) to the result
+ * buffer. As a result of the flushing, the '->nr_accesses' of regions are
+ * initialized to zero.
+ */
+static void damon_test_aggregate(struct kunit *test)
+{
+ struct damon_ctx *ctx = damon_new_ctx();
+ unsigned long target_ids[] = {1, 2, 3};
+ unsigned long saddr[][3] = {{10, 20, 30}, {5, 42, 49}, {13, 33, 55} };
+ unsigned long eaddr[][3] = {{15, 27, 40}, {31, 45, 55}, {23, 44, 66} };
+ unsigned long accesses[][3] = {{42, 95, 84}, {10, 20, 30}, {0, 1, 2} };
+ struct damon_target *t;
+ struct damon_region *r;
+ int it, ir;
+
+ damon_set_targets(ctx, target_ids, 3);
+
+ it = 0;
+ damon_for_each_target(t, ctx) {
+ for (ir = 0; ir < 3; ir++) {
+ r = damon_new_region(saddr[it][ir], eaddr[it][ir]);
+ r->nr_accesses = accesses[it][ir];
+ damon_add_region(r, t);
+ }
+ it++;
+ }
+ kdamond_reset_aggregated(ctx);
+ it = 0;
+ damon_for_each_target(t, ctx) {
+ ir = 0;
+ /* '->nr_accesses' should be zeroed */
+ damon_for_each_region(r, t) {
+ KUNIT_EXPECT_EQ(test, 0u, r->nr_accesses);
+ ir++;
+ }
+ /* regions should be preserved */
+ KUNIT_EXPECT_EQ(test, 3, ir);
+ it++;
+ }
+ /* targets also should be preserved */
+ KUNIT_EXPECT_EQ(test, 3, it);
+
+ damon_destroy_ctx(ctx);
+}
+
+static void damon_test_split_at(struct kunit *test)
+{
+ struct damon_ctx *c = damon_new_ctx();
+ struct damon_target *t;
+ struct damon_region *r;
+
+ t = damon_new_target(42);
+ r = damon_new_region(0, 100);
+ damon_add_region(r, t);
+ damon_split_region_at(c, r, 25);
+ KUNIT_EXPECT_EQ(test, r->ar.start, 0ul);
+ KUNIT_EXPECT_EQ(test, r->ar.end, 25ul);
+
+ r = damon_next_region(r);
+ KUNIT_EXPECT_EQ(test, r->ar.start, 25ul);
+ KUNIT_EXPECT_EQ(test, r->ar.end, 100ul);
+
+ damon_free_target(t);
+ damon_destroy_ctx(c);
+}
+
+static void damon_test_merge_two(struct kunit *test)
+{
+ struct damon_target *t;
+ struct damon_region *r, *r2, *r3;
+ int i;
+
+ t = damon_new_target(42);
+ r = damon_new_region(0, 100);
+ r->nr_accesses = 10;
+ damon_add_region(r, t);
+ r2 = damon_new_region(100, 300);
+ r2->nr_accesses = 20;
+ damon_add_region(r2, t);
+
+ damon_merge_two_regions(r, r2);
+ KUNIT_EXPECT_EQ(test, r->ar.start, 0ul);
+ KUNIT_EXPECT_EQ(test, r->ar.end, 300ul);
+ KUNIT_EXPECT_EQ(test, r->nr_accesses, 16u);
+
+ i = 0;
+ damon_for_each_region(r3, t) {
+ KUNIT_EXPECT_PTR_EQ(test, r, r3);
+ i++;
+ }
+ KUNIT_EXPECT_EQ(test, i, 1);
+
+ damon_free_target(t);
+}
+
+static struct damon_region *__nth_region_of(struct damon_target *t, int idx)
+{
+ struct damon_region *r;
+ unsigned int i = 0;
+
+ damon_for_each_region(r, t) {
+ if (i++ == idx)
+ return r;
+ }
+
+ return NULL;
+}
+
+static void damon_test_merge_regions_of(struct kunit *test)
+{
+ struct damon_target *t;
+ struct damon_region *r;
+ unsigned long sa[] = {0, 100, 114, 122, 130, 156, 170, 184};
+ unsigned long ea[] = {100, 112, 122, 130, 156, 170, 184, 230};
+ unsigned int nrs[] = {0, 0, 10, 10, 20, 30, 1, 2};
+
+ unsigned long saddrs[] = {0, 114, 130, 156, 170};
+ unsigned long eaddrs[] = {112, 130, 156, 170, 230};
+ int i;
+
+ t = damon_new_target(42);
+ for (i = 0; i < ARRAY_SIZE(sa); i++) {
+ r = damon_new_region(sa[i], ea[i]);
+ r->nr_accesses = nrs[i];
+ damon_add_region(r, t);
+ }
+
+ damon_merge_regions_of(t, 9, 9999);
+ /* 0-112, 114-130, 130-156, 156-170 */
+ KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 5u);
+ for (i = 0; i < 5; i++) {
+ r = __nth_region_of(t, i);
+ KUNIT_EXPECT_EQ(test, r->ar.start, saddrs[i]);
+ KUNIT_EXPECT_EQ(test, r->ar.end, eaddrs[i]);
+ }
+ damon_free_target(t);
+}
+
+static void damon_test_split_regions_of(struct kunit *test)
+{
+ struct damon_ctx *c = damon_new_ctx();
+ struct damon_target *t;
+ struct damon_region *r;
+
+ t = damon_new_target(42);
+ r = damon_new_region(0, 22);
+ damon_add_region(r, t);
+ damon_split_regions_of(c, t, 2);
+ KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 2u);
+ damon_free_target(t);
+
+ t = damon_new_target(42);
+ r = damon_new_region(0, 220);
+ damon_add_region(r, t);
+ damon_split_regions_of(c, t, 4);
+ KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 4u);
+ damon_free_target(t);
+ damon_destroy_ctx(c);
+}
+
+static struct kunit_case damon_test_cases[] = {
+ KUNIT_CASE(damon_test_target),
+ KUNIT_CASE(damon_test_regions),
+ KUNIT_CASE(damon_test_aggregate),
+ KUNIT_CASE(damon_test_split_at),
+ KUNIT_CASE(damon_test_merge_two),
+ KUNIT_CASE(damon_test_merge_regions_of),
+ KUNIT_CASE(damon_test_split_regions_of),
+ {},
+};
+
+static struct kunit_suite damon_test_suite = {
+ .name = "damon",
+ .test_cases = damon_test_cases,
+};
+kunit_test_suite(damon_test_suite);
+
+#endif /* _DAMON_CORE_TEST_H */
+
+#endif /* CONFIG_DAMON_KUNIT_TEST */
diff --git a/mm/damon/core.c b/mm/damon/core.c
index cad2b4cee39d..6bfb5d7d9142 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -16,6 +16,11 @@
#define CREATE_TRACE_POINTS
#include <trace/events/damon.h>

+#ifdef CONFIG_DAMON_KUNIT_TEST
+#undef DAMON_MIN_REGION
+#define DAMON_MIN_REGION 1
+#endif
+
/* Get a random number in [l, r) */
#define damon_rand(l, r) (l + prandom_u32_max(r - l))

@@ -709,3 +714,5 @@ static int kdamond_fn(void *data)

do_exit(0);
}
+
+#include "core-test.h"
diff --git a/mm/damon/dbgfs-test.h b/mm/damon/dbgfs-test.h
new file mode 100644
index 000000000000..930e83bceef0
--- /dev/null
+++ b/mm/damon/dbgfs-test.h
@@ -0,0 +1,126 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DAMON Debugfs Interface Unit Tests
+ *
+ * Author: SeongJae Park <[email protected]>
+ */
+
+#ifdef CONFIG_DAMON_DBGFS_KUNIT_TEST
+
+#ifndef _DAMON_DBGFS_TEST_H
+#define _DAMON_DBGFS_TEST_H
+
+#include <kunit/test.h>
+
+static void damon_dbgfs_test_str_to_target_ids(struct kunit *test)
+{
+ char *question;
+ unsigned long *answers;
+ unsigned long expected[] = {12, 35, 46};
+ ssize_t nr_integers = 0, i;
+
+ question = "123";
+ answers = str_to_target_ids(question, strnlen(question, 128),
+ &nr_integers);
+ KUNIT_EXPECT_EQ(test, (ssize_t)1, nr_integers);
+ KUNIT_EXPECT_EQ(test, 123ul, answers[0]);
+ kfree(answers);
+
+ question = "123abc";
+ answers = str_to_target_ids(question, strnlen(question, 128),
+ &nr_integers);
+ KUNIT_EXPECT_EQ(test, (ssize_t)1, nr_integers);
+ KUNIT_EXPECT_EQ(test, 123ul, answers[0]);
+ kfree(answers);
+
+ question = "a123";
+ answers = str_to_target_ids(question, strnlen(question, 128),
+ &nr_integers);
+ KUNIT_EXPECT_EQ(test, (ssize_t)0, nr_integers);
+ kfree(answers);
+
+ question = "12 35";
+ answers = str_to_target_ids(question, strnlen(question, 128),
+ &nr_integers);
+ KUNIT_EXPECT_EQ(test, (ssize_t)2, nr_integers);
+ for (i = 0; i < nr_integers; i++)
+ KUNIT_EXPECT_EQ(test, expected[i], answers[i]);
+ kfree(answers);
+
+ question = "12 35 46";
+ answers = str_to_target_ids(question, strnlen(question, 128),
+ &nr_integers);
+ KUNIT_EXPECT_EQ(test, (ssize_t)3, nr_integers);
+ for (i = 0; i < nr_integers; i++)
+ KUNIT_EXPECT_EQ(test, expected[i], answers[i]);
+ kfree(answers);
+
+ question = "12 35 abc 46";
+ answers = str_to_target_ids(question, strnlen(question, 128),
+ &nr_integers);
+ KUNIT_EXPECT_EQ(test, (ssize_t)2, nr_integers);
+ for (i = 0; i < 2; i++)
+ KUNIT_EXPECT_EQ(test, expected[i], answers[i]);
+ kfree(answers);
+
+ question = "";
+ answers = str_to_target_ids(question, strnlen(question, 128),
+ &nr_integers);
+ KUNIT_EXPECT_EQ(test, (ssize_t)0, nr_integers);
+ kfree(answers);
+
+ question = "\n";
+ answers = str_to_target_ids(question, strnlen(question, 128),
+ &nr_integers);
+ KUNIT_EXPECT_EQ(test, (ssize_t)0, nr_integers);
+ kfree(answers);
+}
+
+static void damon_dbgfs_test_set_targets(struct kunit *test)
+{
+ struct damon_ctx *ctx = dbgfs_new_ctx();
+ unsigned long ids[] = {1, 2, 3};
+ char buf[64];
+
+ /* Make DAMON consider target id as plain number */
+ ctx->primitive.target_valid = NULL;
+ ctx->primitive.cleanup = NULL;
+
+ damon_set_targets(ctx, ids, 3);
+ sprint_target_ids(ctx, buf, 64);
+ KUNIT_EXPECT_STREQ(test, (char *)buf, "1 2 3\n");
+
+ damon_set_targets(ctx, NULL, 0);
+ sprint_target_ids(ctx, buf, 64);
+ KUNIT_EXPECT_STREQ(test, (char *)buf, "\n");
+
+ damon_set_targets(ctx, (unsigned long []){1, 2}, 2);
+ sprint_target_ids(ctx, buf, 64);
+ KUNIT_EXPECT_STREQ(test, (char *)buf, "1 2\n");
+
+ damon_set_targets(ctx, (unsigned long []){2}, 1);
+ sprint_target_ids(ctx, buf, 64);
+ KUNIT_EXPECT_STREQ(test, (char *)buf, "2\n");
+
+ damon_set_targets(ctx, NULL, 0);
+ sprint_target_ids(ctx, buf, 64);
+ KUNIT_EXPECT_STREQ(test, (char *)buf, "\n");
+
+ dbgfs_destroy_ctx(ctx);
+}
+
+static struct kunit_case damon_test_cases[] = {
+ KUNIT_CASE(damon_dbgfs_test_str_to_target_ids),
+ KUNIT_CASE(damon_dbgfs_test_set_targets),
+ {},
+};
+
+static struct kunit_suite damon_test_suite = {
+ .name = "damon-dbgfs",
+ .test_cases = damon_test_cases,
+};
+kunit_test_suite(damon_test_suite);
+
+#endif /* _DAMON_TEST_H */
+
+#endif /* CONFIG_DAMON_KUNIT_TEST */
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 07bc03f7f34d..22e3bb2156e6 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -611,3 +611,5 @@ static int __init damon_dbgfs_init(void)
}

module_init(damon_dbgfs_init);
+
+#include "dbgfs-test.h"
diff --git a/mm/damon/vaddr-test.h b/mm/damon/vaddr-test.h
new file mode 100644
index 000000000000..c9394e1d21d3
--- /dev/null
+++ b/mm/damon/vaddr-test.h
@@ -0,0 +1,328 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Data Access Monitor Unit Tests
+ *
+ * Copyright 2019 Amazon.com, Inc. or its affiliates. All rights reserved.
+ *
+ * Author: SeongJae Park <[email protected]>
+ */
+
+#ifdef CONFIG_DAMON_VADDR_KUNIT_TEST
+
+#ifndef _DAMON_VADDR_TEST_H
+#define _DAMON_VADDR_TEST_H
+
+#include <kunit/test.h>
+
+static void __link_vmas(struct vm_area_struct *vmas, ssize_t nr_vmas)
+{
+ int i, j;
+ unsigned long largest_gap, gap;
+
+ if (!nr_vmas)
+ return;
+
+ for (i = 0; i < nr_vmas - 1; i++) {
+ vmas[i].vm_next = &vmas[i + 1];
+
+ vmas[i].vm_rb.rb_left = NULL;
+ vmas[i].vm_rb.rb_right = &vmas[i + 1].vm_rb;
+
+ largest_gap = 0;
+ for (j = i; j < nr_vmas; j++) {
+ if (j == 0)
+ continue;
+ gap = vmas[j].vm_start - vmas[j - 1].vm_end;
+ if (gap > largest_gap)
+ largest_gap = gap;
+ }
+ vmas[i].rb_subtree_gap = largest_gap;
+ }
+ vmas[i].vm_next = NULL;
+ vmas[i].vm_rb.rb_right = NULL;
+ vmas[i].rb_subtree_gap = 0;
+}
+
+/*
+ * Test __damon_va_three_regions() function
+ *
+ * In case of virtual memory address spaces monitoring, DAMON converts the
+ * complex and dynamic memory mappings of each target task to three
+ * discontiguous regions which cover every mapped areas. However, the three
+ * regions should not include the two biggest unmapped areas in the original
+ * mapping, because the two biggest areas are normally the areas between 1)
+ * heap and the mmap()-ed regions, and 2) the mmap()-ed regions and stack.
+ * Because these two unmapped areas are very huge but obviously never accessed,
+ * covering the region is just a waste.
+ *
+ * '__damon_va_three_regions() receives an address space of a process. It
+ * first identifies the start of mappings, end of mappings, and the two biggest
+ * unmapped areas. After that, based on the information, it constructs the
+ * three regions and returns. For more detail, refer to the comment of
+ * 'damon_init_regions_of()' function definition in 'mm/damon.c' file.
+ *
+ * For example, suppose virtual address ranges of 10-20, 20-25, 200-210,
+ * 210-220, 300-305, and 307-330 (Other comments represent this mappings in
+ * more short form: 10-20-25, 200-210-220, 300-305, 307-330) of a process are
+ * mapped. To cover every mappings, the three regions should start with 10,
+ * and end with 305. The process also has three unmapped areas, 25-200,
+ * 220-300, and 305-307. Among those, 25-200 and 220-300 are the biggest two
+ * unmapped areas, and thus it should be converted to three regions of 10-25,
+ * 200-220, and 300-330.
+ */
+static void damon_test_three_regions_in_vmas(struct kunit *test)
+{
+ struct damon_addr_range regions[3] = {0,};
+ /* 10-20-25, 200-210-220, 300-305, 307-330 */
+ struct vm_area_struct vmas[] = {
+ (struct vm_area_struct) {.vm_start = 10, .vm_end = 20},
+ (struct vm_area_struct) {.vm_start = 20, .vm_end = 25},
+ (struct vm_area_struct) {.vm_start = 200, .vm_end = 210},
+ (struct vm_area_struct) {.vm_start = 210, .vm_end = 220},
+ (struct vm_area_struct) {.vm_start = 300, .vm_end = 305},
+ (struct vm_area_struct) {.vm_start = 307, .vm_end = 330},
+ };
+
+ __link_vmas(vmas, 6);
+
+ __damon_va_three_regions(&vmas[0], regions);
+
+ KUNIT_EXPECT_EQ(test, 10ul, regions[0].start);
+ KUNIT_EXPECT_EQ(test, 25ul, regions[0].end);
+ KUNIT_EXPECT_EQ(test, 200ul, regions[1].start);
+ KUNIT_EXPECT_EQ(test, 220ul, regions[1].end);
+ KUNIT_EXPECT_EQ(test, 300ul, regions[2].start);
+ KUNIT_EXPECT_EQ(test, 330ul, regions[2].end);
+}
+
+static struct damon_region *__nth_region_of(struct damon_target *t, int idx)
+{
+ struct damon_region *r;
+ unsigned int i = 0;
+
+ damon_for_each_region(r, t) {
+ if (i++ == idx)
+ return r;
+ }
+
+ return NULL;
+}
+
+/*
+ * Test 'damon_va_apply_three_regions()'
+ *
+ * test kunit object
+ * regions an array containing start/end addresses of current
+ * monitoring target regions
+ * nr_regions the number of the addresses in 'regions'
+ * three_regions The three regions that need to be applied now
+ * expected start/end addresses of monitoring target regions that
+ * 'three_regions' are applied
+ * nr_expected the number of addresses in 'expected'
+ *
+ * The memory mapping of the target processes changes dynamically. To follow
+ * the change, DAMON periodically reads the mappings, simplifies it to the
+ * three regions, and updates the monitoring target regions to fit in the three
+ * regions. The update of current target regions is the role of
+ * 'damon_va_apply_three_regions()'.
+ *
+ * This test passes the given target regions and the new three regions that
+ * need to be applied to the function and check whether it updates the regions
+ * as expected.
+ */
+static void damon_do_test_apply_three_regions(struct kunit *test,
+ unsigned long *regions, int nr_regions,
+ struct damon_addr_range *three_regions,
+ unsigned long *expected, int nr_expected)
+{
+ struct damon_ctx *ctx = damon_new_ctx();
+ struct damon_target *t;
+ struct damon_region *r;
+ int i;
+
+ t = damon_new_target(42);
+ for (i = 0; i < nr_regions / 2; i++) {
+ r = damon_new_region(regions[i * 2], regions[i * 2 + 1]);
+ damon_add_region(r, t);
+ }
+ damon_add_target(ctx, t);
+
+ damon_va_apply_three_regions(ctx, t, three_regions);
+
+ for (i = 0; i < nr_expected / 2; i++) {
+ r = __nth_region_of(t, i);
+ KUNIT_EXPECT_EQ(test, r->ar.start, expected[i * 2]);
+ KUNIT_EXPECT_EQ(test, r->ar.end, expected[i * 2 + 1]);
+ }
+
+ damon_destroy_ctx(ctx);
+}
+
+/*
+ * This function test most common case where the three big regions are only
+ * slightly changed. Target regions should adjust their boundary (10-20-30,
+ * 50-55, 70-80, 90-100) to fit with the new big regions or remove target
+ * regions (57-79) that now out of the three regions.
+ */
+static void damon_test_apply_three_regions1(struct kunit *test)
+{
+ /* 10-20-30, 50-55-57-59, 70-80-90-100 */
+ unsigned long regions[] = {10, 20, 20, 30, 50, 55, 55, 57, 57, 59,
+ 70, 80, 80, 90, 90, 100};
+ /* 5-27, 45-55, 73-104 */
+ struct damon_addr_range new_three_regions[3] = {
+ (struct damon_addr_range){.start = 5, .end = 27},
+ (struct damon_addr_range){.start = 45, .end = 55},
+ (struct damon_addr_range){.start = 73, .end = 104} };
+ /* 5-20-27, 45-55, 73-80-90-104 */
+ unsigned long expected[] = {5, 20, 20, 27, 45, 55,
+ 73, 80, 80, 90, 90, 104};
+
+ damon_do_test_apply_three_regions(test, regions, ARRAY_SIZE(regions),
+ new_three_regions, expected, ARRAY_SIZE(expected));
+}
+
+/*
+ * Test slightly bigger change. Similar to above, but the second big region
+ * now require two target regions (50-55, 57-59) to be removed.
+ */
+static void damon_test_apply_three_regions2(struct kunit *test)
+{
+ /* 10-20-30, 50-55-57-59, 70-80-90-100 */
+ unsigned long regions[] = {10, 20, 20, 30, 50, 55, 55, 57, 57, 59,
+ 70, 80, 80, 90, 90, 100};
+ /* 5-27, 56-57, 65-104 */
+ struct damon_addr_range new_three_regions[3] = {
+ (struct damon_addr_range){.start = 5, .end = 27},
+ (struct damon_addr_range){.start = 56, .end = 57},
+ (struct damon_addr_range){.start = 65, .end = 104} };
+ /* 5-20-27, 56-57, 65-80-90-104 */
+ unsigned long expected[] = {5, 20, 20, 27, 56, 57,
+ 65, 80, 80, 90, 90, 104};
+
+ damon_do_test_apply_three_regions(test, regions, ARRAY_SIZE(regions),
+ new_three_regions, expected, ARRAY_SIZE(expected));
+}
+
+/*
+ * Test a big change. The second big region has totally freed and mapped to
+ * different area (50-59 -> 61-63). The target regions which were in the old
+ * second big region (50-55-57-59) should be removed and new target region
+ * covering the second big region (61-63) should be created.
+ */
+static void damon_test_apply_three_regions3(struct kunit *test)
+{
+ /* 10-20-30, 50-55-57-59, 70-80-90-100 */
+ unsigned long regions[] = {10, 20, 20, 30, 50, 55, 55, 57, 57, 59,
+ 70, 80, 80, 90, 90, 100};
+ /* 5-27, 61-63, 65-104 */
+ struct damon_addr_range new_three_regions[3] = {
+ (struct damon_addr_range){.start = 5, .end = 27},
+ (struct damon_addr_range){.start = 61, .end = 63},
+ (struct damon_addr_range){.start = 65, .end = 104} };
+ /* 5-20-27, 61-63, 65-80-90-104 */
+ unsigned long expected[] = {5, 20, 20, 27, 61, 63,
+ 65, 80, 80, 90, 90, 104};
+
+ damon_do_test_apply_three_regions(test, regions, ARRAY_SIZE(regions),
+ new_three_regions, expected, ARRAY_SIZE(expected));
+}
+
+/*
+ * Test another big change. Both of the second and third big regions (50-59
+ * and 70-100) has totally freed and mapped to different area (30-32 and
+ * 65-68). The target regions which were in the old second and third big
+ * regions should now be removed and new target regions covering the new second
+ * and third big regions should be crated.
+ */
+static void damon_test_apply_three_regions4(struct kunit *test)
+{
+ /* 10-20-30, 50-55-57-59, 70-80-90-100 */
+ unsigned long regions[] = {10, 20, 20, 30, 50, 55, 55, 57, 57, 59,
+ 70, 80, 80, 90, 90, 100};
+ /* 5-7, 30-32, 65-68 */
+ struct damon_addr_range new_three_regions[3] = {
+ (struct damon_addr_range){.start = 5, .end = 7},
+ (struct damon_addr_range){.start = 30, .end = 32},
+ (struct damon_addr_range){.start = 65, .end = 68} };
+ /* expect 5-7, 30-32, 65-68 */
+ unsigned long expected[] = {5, 7, 30, 32, 65, 68};
+
+ damon_do_test_apply_three_regions(test, regions, ARRAY_SIZE(regions),
+ new_three_regions, expected, ARRAY_SIZE(expected));
+}
+
+static void damon_test_split_evenly(struct kunit *test)
+{
+ struct damon_ctx *c = damon_new_ctx();
+ struct damon_target *t;
+ struct damon_region *r;
+ unsigned long i;
+
+ KUNIT_EXPECT_EQ(test, damon_va_evenly_split_region(c, NULL, 5), -EINVAL);
+
+ t = damon_new_target(42);
+ r = damon_new_region(0, 100);
+ KUNIT_EXPECT_EQ(test, damon_va_evenly_split_region(c, r, 0), -EINVAL);
+
+ damon_add_region(r, t);
+ KUNIT_EXPECT_EQ(test, damon_va_evenly_split_region(c, r, 10), 0);
+ KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 10u);
+
+ i = 0;
+ damon_for_each_region(r, t) {
+ KUNIT_EXPECT_EQ(test, r->ar.start, i++ * 10);
+ KUNIT_EXPECT_EQ(test, r->ar.end, i * 10);
+ }
+ damon_free_target(t);
+
+ t = damon_new_target(42);
+ r = damon_new_region(5, 59);
+ damon_add_region(r, t);
+ KUNIT_EXPECT_EQ(test, damon_va_evenly_split_region(c, r, 5), 0);
+ KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 5u);
+
+ i = 0;
+ damon_for_each_region(r, t) {
+ if (i == 4)
+ break;
+ KUNIT_EXPECT_EQ(test, r->ar.start, 5 + 10 * i++);
+ KUNIT_EXPECT_EQ(test, r->ar.end, 5 + 10 * i);
+ }
+ KUNIT_EXPECT_EQ(test, r->ar.start, 5 + 10 * i);
+ KUNIT_EXPECT_EQ(test, r->ar.end, 59ul);
+ damon_free_target(t);
+
+ t = damon_new_target(42);
+ r = damon_new_region(5, 6);
+ damon_add_region(r, t);
+ KUNIT_EXPECT_EQ(test, damon_va_evenly_split_region(c, r, 2), -EINVAL);
+ KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1u);
+
+ damon_for_each_region(r, t) {
+ KUNIT_EXPECT_EQ(test, r->ar.start, 5ul);
+ KUNIT_EXPECT_EQ(test, r->ar.end, 6ul);
+ }
+ damon_free_target(t);
+ damon_destroy_ctx(c);
+}
+
+static struct kunit_case damon_test_cases[] = {
+ KUNIT_CASE(damon_test_three_regions_in_vmas),
+ KUNIT_CASE(damon_test_apply_three_regions1),
+ KUNIT_CASE(damon_test_apply_three_regions2),
+ KUNIT_CASE(damon_test_apply_three_regions3),
+ KUNIT_CASE(damon_test_apply_three_regions4),
+ KUNIT_CASE(damon_test_split_evenly),
+ {},
+};
+
+static struct kunit_suite damon_test_suite = {
+ .name = "damon-primitives",
+ .test_cases = damon_test_cases,
+};
+kunit_test_suite(damon_test_suite);
+
+#endif /* _DAMON_VADDR_TEST_H */
+
+#endif /* CONFIG_DAMON_VADDR_KUNIT_TEST */
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 3bc9dc9f0656..a0cd006b3ec5 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -15,6 +15,11 @@
#include <linux/sched/mm.h>
#include <linux/slab.h>

+#ifdef CONFIG_DAMON_VADDR_KUNIT_TEST
+#undef DAMON_MIN_REGION
+#define DAMON_MIN_REGION 1
+#endif
+
/* Get a random number in [l, r) */
#define damon_rand(l, r) (l + prandom_u32_max(r - l))

@@ -614,3 +619,5 @@ void damon_va_set_primitives(struct damon_ctx *ctx)
ctx->primitive.target_valid = damon_va_target_valid;
ctx->primitive.cleanup = damon_va_cleanup;
}
+
+#include "vaddr-test.h"
--
2.17.1

2021-06-21 08:33:19

by SeongJae Park

Subject: [PATCH v31 10/13] Documentation: Add documents for DAMON

From: SeongJae Park <[email protected]>

This commit adds documents for DAMON under
`Documentation/admin-guide/mm/damon/` and `Documentation/vm/damon/`.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
Reviewed-by: Markus Boehme <[email protected]>
---
Documentation/admin-guide/mm/damon/index.rst | 15 ++
Documentation/admin-guide/mm/damon/start.rst | 114 +++++++++++++
Documentation/admin-guide/mm/damon/usage.rst | 112 +++++++++++++
Documentation/admin-guide/mm/index.rst | 1 +
Documentation/vm/damon/api.rst | 20 +++
Documentation/vm/damon/design.rst | 166 +++++++++++++++++++
Documentation/vm/damon/faq.rst | 51 ++++++
Documentation/vm/damon/index.rst | 30 ++++
Documentation/vm/index.rst | 1 +
9 files changed, 510 insertions(+)
create mode 100644 Documentation/admin-guide/mm/damon/index.rst
create mode 100644 Documentation/admin-guide/mm/damon/start.rst
create mode 100644 Documentation/admin-guide/mm/damon/usage.rst
create mode 100644 Documentation/vm/damon/api.rst
create mode 100644 Documentation/vm/damon/design.rst
create mode 100644 Documentation/vm/damon/faq.rst
create mode 100644 Documentation/vm/damon/index.rst

diff --git a/Documentation/admin-guide/mm/damon/index.rst b/Documentation/admin-guide/mm/damon/index.rst
new file mode 100644
index 000000000000..8c5dde3a5754
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/index.rst
@@ -0,0 +1,15 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================
+Monitoring Data Accesses
+========================
+
+:doc:`DAMON </vm/damon/index>` allows light-weight data access monitoring.
+Using DAMON, users can analyze the memory access patterns of their systems and
+optimize those.
+
+.. toctree::
+ :maxdepth: 2
+
+ start
+ usage
diff --git a/Documentation/admin-guide/mm/damon/start.rst b/Documentation/admin-guide/mm/damon/start.rst
new file mode 100644
index 000000000000..d5eb89a8fc38
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/start.rst
@@ -0,0 +1,114 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Getting Started
+===============
+
+This document briefly describes how you can use DAMON by demonstrating its
+default user space tool. Please note that this document describes only a part
+of its features for brevity. Please refer to :doc:`usage` for more details.
+
+
+TL; DR
+======
+
+Follow the commands below to monitor and visualize the memory access pattern of
+your workload. ::
+
+ # # build the kernel with CONFIG_DAMON_*=y, install it, and reboot
+ # mount -t debugfs none /sys/kernel/debug/
+ # git clone https://github.com/awslabs/damo
+ # ./damo/damo record $(pidof <your workload>)
+ # ./damo/damo report heat --plot_ascii
+
+The final command draws the access heatmap of ``<your workload>``. The heatmap
+shows which memory region (x-axis) is accessed when (y-axis) and how frequently
+(number; the higher the more accesses have been observed). ::
+
+ 111111111111111111111111111111111111111111111111111111110000
+ 111121111111111111111111111111211111111111111111111111110000
+ 000000000000000000000000000000000000000000000000001555552000
+ 000000000000000000000000000000000000000000000222223555552000
+ 000000000000000000000000000000000000000011111677775000000000
+ 000000000000000000000000000000000000000488888000000000000000
+ 000000000000000000000000000000000177888400000000000000000000
+ 000000000000000000000000000046666522222100000000000000000000
+ 000000000000000000000014444344444300000000000000000000000000
+ 000000000000000002222245555510000000000000000000000000000000
+ # access_frequency: 0 1 2 3 4 5 6 7 8 9
+ # x-axis: space (140286319947776-140286426374096: 101.496 MiB)
+ # y-axis: time (605442256436361-605479951866441: 37.695430s)
+ # resolution: 60x10 (1.692 MiB and 3.770s for each character)
+
+
+Prerequisites
+=============
+
+Kernel
+------
+
+You should first ensure your system is running on a kernel built with
+``CONFIG_DAMON_*=y``.
+
+
+User Space Tool
+---------------
+
+For the demonstration, we will use the default user space tool for DAMON,
+called DAMON Operator (DAMO). It is available at
+https://github.com/awslabs/damo. The examples below assume that ``damo`` is on
+your ``$PATH``. It's not mandatory, though.
+
+Because DAMO is using the debugfs interface (refer to :doc:`usage` for the
+detail) of DAMON, you should ensure debugfs is mounted. Mount it manually as
+below::
+
+ # mount -t debugfs none /sys/kernel/debug/
+
+or append the following line to your ``/etc/fstab`` file so that your system
+can automatically mount debugfs upon booting::
+
+ debugfs /sys/kernel/debug debugfs defaults 0 0
+
+
+Recording Data Access Patterns
+==============================
+
+The commands below record the memory access patterns of a program and save the
+monitoring results to a file. ::
+
+ $ git clone https://github.com/sjp38/masim
+ $ cd masim; make; ./masim ./configs/zigzag.cfg &
+ $ sudo damo record -o damon.data $(pidof masim)
+
+The first two lines of the commands download an artificial memory access
+generator program and run it in the background. The generator will repeatedly
+access two 100 MiB sized memory regions one by one. You can substitute this
+with your real workload. The last line asks ``damo`` to record the access
+pattern in the ``damon.data`` file.
+
+
+Visualizing Recorded Patterns
+=============================
+
+The following three commands visualize the recorded access patterns and save
+the results as separate image files. ::
+
+ $ damo report heats --heatmap access_pattern_heatmap.png
+ $ damo report wss --range 0 101 1 --plot wss_dist.png
+ $ damo report wss --range 0 101 1 --sortby time --plot wss_chron_change.png
+
+- ``access_pattern_heatmap.png`` will visualize the data access pattern in a
+ heatmap, showing which memory region (y-axis) got accessed when (x-axis)
+ and how frequently (color).
+- ``wss_dist.png`` will show the distribution of the working set size.
+- ``wss_chron_change.png`` will show how the working set size has
+ chronologically changed.
+
+You can view the visualizations of this example workload at [1]_.
+Visualizations of other realistic workloads are available at [2]_ [3]_ [4]_.
+
+.. [1] https://damonitor.github.io/doc/html/v17/admin-guide/mm/damon/start.html#visualizing-recorded-patterns
+.. [2] https://damonitor.github.io/test/result/visual/latest/rec.heatmap.1.png.html
+.. [3] https://damonitor.github.io/test/result/visual/latest/rec.wss_sz.png.html
+.. [4] https://damonitor.github.io/test/result/visual/latest/rec.wss_time.png.html
diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
new file mode 100644
index 000000000000..a72cda374aba
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -0,0 +1,112 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Detailed Usages
+===============
+
+DAMON provides below three interfaces for different users.
+
+- *DAMON user space tool.*
+ This is for privileged people such as system administrators who want a
+ just-working human-friendly interface. Using this, users can use the DAMON’s
+ major features in a human-friendly way. It may not be highly tuned for
+ special cases, though. It supports only virtual address spaces monitoring.
+- *debugfs interface.*
+ This is for privileged user space programmers who want more optimized use of
+ DAMON. Using this, users can use DAMON’s major features by reading
+ from and writing to special debugfs files. Therefore, you can write and use
+ your personalized DAMON debugfs wrapper programs that reads/writes the
+ debugfs files instead of you. The DAMON user space tool is also a reference
+ implementation of such programs. It supports only virtual address spaces
+ monitoring.
+- *Kernel Space Programming Interface.*
+ This is for kernel space programmers. Using this, users can utilize every
+ feature of DAMON most flexibly and efficiently by writing kernel space
+ DAMON application programs for you. You can even extend DAMON for various
+ address spaces.
+
+Nevertheless, you could write your own user space tool using the debugfs
+interface. A reference implementation is available at
+https://github.com/awslabs/damo. If you are a kernel programmer, you could
+refer to :doc:`/vm/damon/api` for the kernel space programming interface. For
+the reason, this document describes only the debugfs interface
+
+debugfs Interface
+=================
+
+DAMON exports three files, ``attrs``, ``target_ids``, and ``monitor_on`` under
+its debugfs directory, ``<debugfs>/damon/``.
+
+
+Attributes
+----------
+
+Users can get and set the ``sampling interval``, ``aggregation interval``,
+``regions update interval``, and min/max number of monitoring target regions by
+reading from and writing to the ``attrs`` file. To know about the monitoring
+attributes in detail, please refer to the :doc:`/vm/damon/design`. For
+example, below commands set those values to 5 ms, 100 ms, 1,000 ms, 10 and
+1000, and then check it again::
+
+ # cd <debugfs>/damon
+ # echo 5000 100000 1000000 10 1000 > attrs
+ # cat attrs
+ 5000 100000 1000000 10 1000
+
+
+Target IDs
+----------
+
+Some types of address spaces supports multiple monitoring target. For example,
+the virtual memory address spaces monitoring can have multiple processes as the
+monitoring targets. Users can set the targets by writing relevant id values of
+the targets to, and get the ids of the current targets by reading from the
+``target_ids`` file. In case of the virtual address spaces monitoring, the
+values should be pids of the monitoring target processes. For example, below
+commands set processes having pids 42 and 4242 as the monitoring targets and
+check it again::
+
+ # cd <debugfs>/damon
+ # echo 42 4242 > target_ids
+ # cat target_ids
+ 42 4242
+
+Note that setting the target ids doesn't start the monitoring.
+
+
+Turning On/Off
+--------------
+
+Setting the files as described above doesn't incur effect unless you explicitly
+start the monitoring. You can start, stop, and check the current status of the
+monitoring by writing to and reading from the ``monitor_on`` file. Writing
+``on`` to the file starts the monitoring of the targets with the attributes.
+Writing ``off`` to the file stops those. DAMON also stops if every target
+process is terminated. Below example commands turn on, off, and check the
+status of DAMON::
+
+ # cd <debugfs>/damon
+ # echo on > monitor_on
+ # echo off > monitor_on
+ # cat monitor_on
+ off
+
+Please note that you cannot write to the above-mentioned debugfs files while
+the monitoring is turned on. If you write to the files while DAMON is running,
+an error code such as ``-EBUSY`` will be returned.
+
+
+Tracepoint for Monitoring Results
+=================================
+
+DAMON provides the monitoring results via a tracepoint,
+``damon:damon_aggregated``. While the monitoring is turned on, you could
+record the tracepoint events and show results using tracepoint supporting tools
+like ``perf``. For example::
+
+ # echo on > monitor_on
+ # perf record -e damon:damon_aggregated &
+ # sleep 5
+ # kill 9 $(pidof perf)
+ # echo off > monitor_on
+ # perf script
diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst
index 4b14d8b50e9e..cbd19d5e625f 100644
--- a/Documentation/admin-guide/mm/index.rst
+++ b/Documentation/admin-guide/mm/index.rst
@@ -27,6 +27,7 @@ the Linux memory management.

concepts
cma_debugfs
+ damon/index
hugetlbpage
idle_page_tracking
ksm
diff --git a/Documentation/vm/damon/api.rst b/Documentation/vm/damon/api.rst
new file mode 100644
index 000000000000..08f34df45523
--- /dev/null
+++ b/Documentation/vm/damon/api.rst
@@ -0,0 +1,20 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+API Reference
+=============
+
+Kernel space programs can use every feature of DAMON using below APIs. All you
+need to do is including ``damon.h``, which is located in ``include/linux/`` of
+the source tree.
+
+Structures
+==========
+
+.. kernel-doc:: include/linux/damon.h
+
+
+Functions
+=========
+
+.. kernel-doc:: mm/damon/core.c
diff --git a/Documentation/vm/damon/design.rst b/Documentation/vm/damon/design.rst
new file mode 100644
index 000000000000..b05159c295f4
--- /dev/null
+++ b/Documentation/vm/damon/design.rst
@@ -0,0 +1,166 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======
+Design
+======
+
+Configurable Layers
+===================
+
+DAMON provides data access monitoring functionality while making the accuracy
+and the overhead controllable. The fundamental access monitorings require
+primitives that dependent on and optimized for the target address space. On
+the other hand, the accuracy and overhead tradeoff mechanism, which is the core
+of DAMON, is in the pure logic space. DAMON separates the two parts in
+different layers and defines its interface to allow various low level
+primitives implementations configurable with the core logic.
+
+Due to this separated design and the configurable interface, users can extend
+DAMON for any address space by configuring the core logics with appropriate low
+level primitive implementations. If appropriate one is not provided, users can
+implement the primitives on their own.
+
+For example, physical memory, virtual memory, swap space, those for specific
+processes, NUMA nodes, files, and backing memory devices would be supportable.
+Also, if some architectures or devices support special optimized access check
+primitives, those will be easily configurable.
+
+
+Reference Implementations of Address Space Specific Primitives
+==============================================================
+
+The low level primitives for the fundamental access monitoring are defined in
+two parts:
+
+1. Identification of the monitoring target address range for the address space.
+2. Access check of specific address range in the target space.
+
+DAMON currently provides the implementation of the primitives for only the
+virtual address spaces. Below two subsections describe how it works.
+
+
+VMA-based Target Address Range Construction
+-------------------------------------------
+
+Only small parts in the super-huge virtual address space of the processes are
+mapped to the physical memory and accessed. Thus, tracking the unmapped
+address regions is just wasteful. However, because DAMON can deal with some
+level of noise using the adaptive regions adjustment mechanism, tracking every
+mapping is not strictly required but could even incur a high overhead in some
+cases. That said, too huge unmapped areas inside the monitoring target should
+be removed to not take the time for the adaptive mechanism.
+
+For the reason, this implementation converts the complex mappings to three
+distinct regions that cover every mapped area of the address space. The two
+gaps between the three regions are the two biggest unmapped areas in the given
+address space. The two biggest unmapped areas would be the gap between the
+heap and the uppermost mmap()-ed region, and the gap between the lowermost
+mmap()-ed region and the stack in most of the cases. Because these gaps are
+exceptionally huge in usual address spaces, excluding these will be sufficient
+to make a reasonable trade-off. Below shows this in detail::
+
+ <heap>
+ <BIG UNMAPPED REGION 1>
+ <uppermost mmap()-ed region>
+ (small mmap()-ed regions and munmap()-ed regions)
+ <lowermost mmap()-ed region>
+ <BIG UNMAPPED REGION 2>
+ <stack>
+
+
+PTE Accessed-bit Based Access Check
+-----------------------------------
+
+The implementation for the virtual address space uses PTE Accessed-bit for
+basic access checks. It finds the relevant PTE Accessed bit from the address
+by walking the page table for the target task of the address. In this way, the
+implementation finds and clears the bit for next sampling target address and
+checks whether the bit set again after one sampling period. This could disturb
+other kernel subsystems using the Accessed bits, namely Idle page tracking and
+the reclaim logic. To avoid such disturbances, DAMON makes it mutually
+exclusive with Idle page tracking and uses ``PG_idle`` and ``PG_young`` page
+flags to solve the conflict with the reclaim logic, as Idle page tracking does.
+
+
+Address Space Independent Core Mechanisms
+=========================================
+
+Below four sections describe each of the DAMON core mechanisms and the five
+monitoring attributes, ``sampling interval``, ``aggregation interval``,
+``regions update interval``, ``minimum number of regions``, and ``maximum
+number of regions``.
+
+
+Access Frequency Monitoring
+---------------------------
+
+The output of DAMON says what pages are how frequently accessed for a given
+duration. The resolution of the access frequency is controlled by setting
+``sampling interval`` and ``aggregation interval``. In detail, DAMON checks
+access to each page per ``sampling interval`` and aggregates the results. In
+other words, counts the number of the accesses to each page. After each
+``aggregation interval`` passes, DAMON calls callback functions that previously
+registered by users so that users can read the aggregated results and then
+clears the results. This can be described in below simple pseudo-code::
+
+ while monitoring_on:
+ for page in monitoring_target:
+ if accessed(page):
+ nr_accesses[page] += 1
+ if time() % aggregation_interval == 0:
+ for callback in user_registered_callbacks:
+ callback(monitoring_target, nr_accesses)
+ for page in monitoring_target:
+ nr_accesses[page] = 0
+ sleep(sampling interval)
+
+The monitoring overhead of this mechanism will arbitrarily increase as the
+size of the target workload grows.
+
+
+Region Based Sampling
+---------------------
+
+To avoid the unbounded increase of the overhead, DAMON groups adjacent pages
+that assumed to have the same access frequencies into a region. As long as the
+assumption (pages in a region have the same access frequencies) is kept, only
+one page in the region is required to be checked. Thus, for each ``sampling
+interval``, DAMON randomly picks one page in each region, waits for one
+``sampling interval``, checks whether the page is accessed meanwhile, and
+increases the access frequency of the region if so. Therefore, the monitoring
+overhead is controllable by setting the number of regions. DAMON allows users
+to set the minimum and the maximum number of regions for the trade-off.
+
+This scheme, however, cannot preserve the quality of the output if the
+assumption is not guaranteed.
+
+
+Adaptive Regions Adjustment
+---------------------------
+
+Even somehow the initial monitoring target regions are well constructed to
+fulfill the assumption (pages in same region have similar access frequencies),
+the data access pattern can be dynamically changed. This will result in low
+monitoring quality. To keep the assumption as much as possible, DAMON
+adaptively merges and splits each region based on their access frequency.
+
+For each ``aggregation interval``, it compares the access frequencies of
+adjacent regions and merges those if the frequency difference is small. Then,
+after it reports and clears the aggregated access frequency of each region, it
+splits each region into two or three regions if the total number of regions
+will not exceed the user-specified maximum number of regions after the split.
+
+In this way, DAMON provides its best-effort quality and minimal overhead while
+keeping the bounds users set for their trade-off.
+
+
+Dynamic Target Space Updates Handling
+-------------------------------------
+
+The monitoring target address range could dynamically changed. For example,
+virtual memory could be dynamically mapped and unmapped. Physical memory could
+be hot-plugged.
+
+As the changes could be quite frequent in some cases, DAMON checks the dynamic
+memory mapping changes and applies it to the abstracted target area only for
+each of a user-specified time interval (``regions update interval``).
diff --git a/Documentation/vm/damon/faq.rst b/Documentation/vm/damon/faq.rst
new file mode 100644
index 000000000000..cb3d8b585a8b
--- /dev/null
+++ b/Documentation/vm/damon/faq.rst
@@ -0,0 +1,51 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+Frequently Asked Questions
+==========================
+
+Why a new subsystem, instead of extending perf or other user space tools?
+=========================================================================
+
+First, because it needs to be lightweight as much as possible so that it can be
+used online, any unnecessary overhead such as kernel - user space context
+switching cost should be avoided. Second, DAMON aims to be used by other
+programs including the kernel. Therefore, having a dependency on specific
+tools like perf is not desirable. These are the two biggest reasons why DAMON
+is implemented in the kernel space.
+
+
+Can 'idle pages tracking' or 'perf mem' substitute DAMON?
+=========================================================
+
+Idle page tracking is a low level primitive for access check of the physical
+address space. 'perf mem' is similar, though it can use sampling to minimize
+the overhead. On the other hand, DAMON is a higher-level framework for the
+monitoring of various address spaces. It is focused on memory management
+optimization and provides sophisticated accuracy/overhead handling mechanisms.
+Therefore, 'idle pages tracking' and 'perf mem' could provide a subset of
+DAMON's output, but cannot substitute DAMON.
+
+
+Does DAMON support virtual memory only?
+=======================================
+
+No. The core of the DAMON is address space independent. The address space
+specific low level primitive parts including monitoring target regions
+constructions and actual access checks can be implemented and configured on the
+DAMON core by the users. In this way, DAMON users can monitor any address
+space with any access check technique.
+
+Nonetheless, DAMON provides vma tracking and PTE Accessed bit check based
+implementations of the address space dependent functions for the virtual memory
+by default, for a reference and convenient use. In near future, we will
+provide those for physical memory address space.
+
+
+Can I simply monitor page granularity?
+======================================
+
+Yes. You can do so by setting the ``min_nr_regions`` attribute higher than the
+working set size divided by the page size. Because the monitoring target
+regions size is forced to be ``>=page size``, the region split will make no
+effect.
diff --git a/Documentation/vm/damon/index.rst b/Documentation/vm/damon/index.rst
new file mode 100644
index 000000000000..a2858baf3bf1
--- /dev/null
+++ b/Documentation/vm/damon/index.rst
@@ -0,0 +1,30 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+DAMON: Data Access MONitor
+==========================
+
+DAMON is a data access monitoring framework subsystem for the Linux kernel.
+The core mechanisms of DAMON (refer to :doc:`design` for the detail) make it
+
+ - *accurate* (the monitoring output is useful enough for DRAM level memory
+ management; It might not appropriate for CPU Cache levels, though),
+ - *light-weight* (the monitoring overhead is low enough to be applied online),
+ and
+ - *scalable* (the upper-bound of the overhead is in constant range regardless
+ of the size of target workloads).
+
+Using this framework, therefore, the kernel's memory management mechanisms can
+make advanced decisions. Experimental memory management optimization works
+that incurring high data accesses monitoring overhead could implemented again.
+In user space, meanwhile, users who have some special workloads can write
+personalized applications for better understanding and optimizations of their
+workloads and systems.
+
+.. toctree::
+ :maxdepth: 2
+
+ faq
+ design
+ api
+ plans
diff --git a/Documentation/vm/index.rst b/Documentation/vm/index.rst
index eff5fbd492d0..b51f0d8992f8 100644
--- a/Documentation/vm/index.rst
+++ b/Documentation/vm/index.rst
@@ -32,6 +32,7 @@ descriptions of data structures and algorithms.
arch_pgtable_helpers
balance
cleancache
+ damon/index
free_page_reporting
frontswap
highmem
--
2.17.1

2021-06-21 08:33:23

by SeongJae Park

Subject: [PATCH v31 02/13] mm/damon/core: Implement region-based sampling

From: SeongJae Park <[email protected]>

To avoid the unbounded increase of the overhead, DAMON groups adjacent
pages that are assumed to have the same access frequencies into a
region. As long as the assumption (pages in a region have the same
access frequencies) is kept, only one page in the region is required to
be checked. Thus, for each ``sampling interval``,

1. the 'prepare_access_checks' primitive picks one page in each region,
2. waits for one ``sampling interval``,
3. checks whether the page is accessed meanwhile, and
4. increases the access count of the region if so.

Therefore, the monitoring overhead is controllable by adjusting the
number of regions. DAMON allows both the underlying primitives and user
callbacks to adjust regions for the trade-off. In other words, this
commit makes DAMON to use not only time-based sampling but also
space-based sampling.

This scheme, however, cannot preserve the quality of the output if the
assumption is not guaranteed. Next commit will address this problem.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Leonard Foerster <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
include/linux/damon.h | 77 ++++++++++++++++++++++-
mm/damon/core.c | 143 ++++++++++++++++++++++++++++++++++++++++--
2 files changed, 213 insertions(+), 7 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 2f652602b1ea..67db309ad61b 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -12,6 +12,48 @@
#include <linux/time64.h>
#include <linux/types.h>

+/**
+ * struct damon_addr_range - Represents an address region of [@start, @end).
+ * @start: Start address of the region (inclusive).
+ * @end: End address of the region (exclusive).
+ */
+struct damon_addr_range {
+ unsigned long start;
+ unsigned long end;
+};
+
+/**
+ * struct damon_region - Represents a monitoring target region.
+ * @ar: The address range of the region.
+ * @sampling_addr: Address of the sample for the next access check.
+ * @nr_accesses: Access frequency of this region.
+ * @list: List head for siblings.
+ */
+struct damon_region {
+ struct damon_addr_range ar;
+ unsigned long sampling_addr;
+ unsigned int nr_accesses;
+ struct list_head list;
+};
+
+/**
+ * struct damon_target - Represents a monitoring target.
+ * @id: Unique identifier for this target.
+ * @regions_list: Head of the monitoring target regions of this target.
+ * @list: List head for siblings.
+ *
+ * Each monitoring context could have multiple targets. For example, a context
+ * for virtual memory address spaces could have multiple target processes. The
+ * @id of each target should be unique among the targets of the context. For
+ * example, in the virtual address monitoring context, it could be a pidfd or
+ * an address of an mm_struct.
+ */
+struct damon_target {
+ unsigned long id;
+ struct list_head regions_list;
+ struct list_head list;
+};
+
struct damon_ctx;

/**
@@ -36,7 +78,7 @@ struct damon_ctx;
*
* @init should initialize primitive-internal data structures. For example,
* this could be used to construct proper monitoring target regions and link
- * those to @damon_ctx.target.
+ * those to @damon_ctx.adaptive_targets.
* @update should update the primitive-internal data structures. For example,
* this could be used to update monitoring target regions for current status.
* @prepare_access_checks should manipulate the monitoring regions to be
@@ -130,7 +172,7 @@ struct damon_callback {
* @primitive: Set of monitoring primitives for given use cases.
* @callback: Set of callbacks for monitoring events notifications.
*
- * @target: Pointer to the user-defined monitoring target.
+ * @region_targets: Head of monitoring targets (&damon_target) list.
*/
struct damon_ctx {
unsigned long sample_interval;
@@ -149,11 +191,40 @@ struct damon_ctx {
struct damon_primitive primitive;
struct damon_callback callback;

- void *target;
+ struct list_head region_targets;
};

+#define damon_next_region(r) \
+ (container_of(r->list.next, struct damon_region, list))
+
+#define damon_prev_region(r) \
+ (container_of(r->list.prev, struct damon_region, list))
+
+#define damon_for_each_region(r, t) \
+ list_for_each_entry(r, &t->regions_list, list)
+
+#define damon_for_each_region_safe(r, next, t) \
+ list_for_each_entry_safe(r, next, &t->regions_list, list)
+
+#define damon_for_each_target(t, ctx) \
+ list_for_each_entry(t, &(ctx)->region_targets, list)
+
+#define damon_for_each_target_safe(t, next, ctx) \
+ list_for_each_entry_safe(t, next, &(ctx)->region_targets, list)
+
#ifdef CONFIG_DAMON

+struct damon_region *damon_new_region(unsigned long start, unsigned long end);
+inline void damon_insert_region(struct damon_region *r,
+ struct damon_region *prev, struct damon_region *next);
+void damon_add_region(struct damon_region *r, struct damon_target *t);
+void damon_destroy_region(struct damon_region *r);
+
+struct damon_target *damon_new_target(unsigned long id);
+void damon_add_target(struct damon_ctx *ctx, struct damon_target *t);
+void damon_free_target(struct damon_target *t);
+void damon_destroy_target(struct damon_target *t);
+
struct damon_ctx *damon_new_ctx(void);
void damon_destroy_ctx(struct damon_ctx *ctx);
int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 693e51ebc05a..94db494dcf70 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -15,6 +15,101 @@
static DEFINE_MUTEX(damon_lock);
static int nr_running_ctxs;

+/*
+ * Construct a damon_region struct
+ *
+ * Returns the pointer to the new struct if success, or NULL otherwise
+ */
+struct damon_region *damon_new_region(unsigned long start, unsigned long end)
+{
+ struct damon_region *region;
+
+ region = kmalloc(sizeof(*region), GFP_KERNEL);
+ if (!region)
+ return NULL;
+
+ region->ar.start = start;
+ region->ar.end = end;
+ region->nr_accesses = 0;
+ INIT_LIST_HEAD(&region->list);
+
+ return region;
+}
+
+/*
+ * Add a region between two other regions
+ */
+inline void damon_insert_region(struct damon_region *r,
+ struct damon_region *prev, struct damon_region *next)
+{
+ __list_add(&r->list, &prev->list, &next->list);
+}
+
+void damon_add_region(struct damon_region *r, struct damon_target *t)
+{
+ list_add_tail(&r->list, &t->regions_list);
+}
+
+static void damon_del_region(struct damon_region *r)
+{
+ list_del(&r->list);
+}
+
+static void damon_free_region(struct damon_region *r)
+{
+ kfree(r);
+}
+
+void damon_destroy_region(struct damon_region *r)
+{
+ damon_del_region(r);
+ damon_free_region(r);
+}
+
+/*
+ * Construct a damon_target struct
+ *
+ * Returns the pointer to the new struct if success, or NULL otherwise
+ */
+struct damon_target *damon_new_target(unsigned long id)
+{
+ struct damon_target *t;
+
+ t = kmalloc(sizeof(*t), GFP_KERNEL);
+ if (!t)
+ return NULL;
+
+ t->id = id;
+ INIT_LIST_HEAD(&t->regions_list);
+
+ return t;
+}
+
+void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
+{
+ list_add_tail(&t->list, &ctx->region_targets);
+}
+
+static void damon_del_target(struct damon_target *t)
+{
+ list_del(&t->list);
+}
+
+void damon_free_target(struct damon_target *t)
+{
+ struct damon_region *r, *next;
+
+ damon_for_each_region_safe(r, next, t)
+ damon_free_region(r);
+ kfree(t);
+}
+
+void damon_destroy_target(struct damon_target *t)
+{
+ damon_del_target(t);
+ damon_free_target(t);
+}
+
struct damon_ctx *damon_new_ctx(void)
{
struct damon_ctx *ctx;
@@ -32,15 +127,27 @@ struct damon_ctx *damon_new_ctx(void)

mutex_init(&ctx->kdamond_lock);

- ctx->target = NULL;
+ INIT_LIST_HEAD(&ctx->region_targets);

return ctx;
}

-void damon_destroy_ctx(struct damon_ctx *ctx)
+static void damon_destroy_targets(struct damon_ctx *ctx)
{
- if (ctx->primitive.cleanup)
+ struct damon_target *t, *next_t;
+
+ if (ctx->primitive.cleanup) {
ctx->primitive.cleanup(ctx);
+ return;
+ }
+
+ damon_for_each_target_safe(t, next_t, ctx)
+ damon_destroy_target(t);
+}
+
+void damon_destroy_ctx(struct damon_ctx *ctx)
+{
+ damon_destroy_targets(ctx);
kfree(ctx);
}

@@ -217,6 +324,21 @@ static bool kdamond_aggregate_interval_passed(struct damon_ctx *ctx)
ctx->aggr_interval);
}

+/*
+ * Reset the aggregated monitoring results ('nr_accesses' of each region).
+ */
+static void kdamond_reset_aggregated(struct damon_ctx *c)
+{
+ struct damon_target *t;
+
+ damon_for_each_target(t, c) {
+ struct damon_region *r;
+
+ damon_for_each_region(r, t)
+ r->nr_accesses = 0;
+ }
+}
+
/*
* Check whether it is time to check and apply the target monitoring regions
*
@@ -238,6 +360,7 @@ static bool kdamond_need_update_primitive(struct damon_ctx *ctx)
*/
static bool kdamond_need_stop(struct damon_ctx *ctx)
{
+ struct damon_target *t;
bool stop;

mutex_lock(&ctx->kdamond_lock);
@@ -249,7 +372,12 @@ static bool kdamond_need_stop(struct damon_ctx *ctx)
if (!ctx->primitive.target_valid)
return false;

- return !ctx->primitive.target_valid(ctx->target);
+ damon_for_each_target(t, ctx) {
+ if (ctx->primitive.target_valid(t))
+ return false;
+ }
+
+ return true;
}

static void set_kdamond_stop(struct damon_ctx *ctx)
@@ -265,6 +393,8 @@ static void set_kdamond_stop(struct damon_ctx *ctx)
static int kdamond_fn(void *data)
{
struct damon_ctx *ctx = (struct damon_ctx *)data;
+ struct damon_target *t;
+ struct damon_region *r, *next;

pr_info("kdamond (%d) starts\n", ctx->kdamond->pid);

@@ -289,6 +419,7 @@ static int kdamond_fn(void *data)
if (ctx->callback.after_aggregation &&
ctx->callback.after_aggregation(ctx))
set_kdamond_stop(ctx);
+ kdamond_reset_aggregated(ctx);
if (ctx->primitive.reset_aggregated)
ctx->primitive.reset_aggregated(ctx);
}
@@ -298,6 +429,10 @@ static int kdamond_fn(void *data)
ctx->primitive.update(ctx);
}
}
+ damon_for_each_target(t, ctx) {
+ damon_for_each_region_safe(r, next, t)
+ damon_destroy_region(r);
+ }

if (ctx->callback.before_terminate &&
ctx->callback.before_terminate(ctx))
--
2.17.1

2021-06-21 08:33:32

by SeongJae Park

Subject: [PATCH v31 03/13] mm/damon: Adaptively adjust regions

From: SeongJae Park <[email protected]>

Even somehow the initial monitoring target regions are well constructed
to fulfill the assumption (pages in same region have similar access
frequencies), the data access pattern can be dynamically changed. This
will result in low monitoring quality. To keep the assumption as much
as possible, DAMON adaptively merges and splits each region based on
their access frequency.

For each ``aggregation interval``, it compares the access frequencies of
adjacent regions and merges those if the frequency difference is small.
Then, after it reports and clears the aggregated access frequency of
each region, it splits each region into two or three regions if the
total number of regions will not exceed the user-specified maximum
number of regions after the split.

In this way, DAMON provides its best-effort quality and minimal overhead
while keeping the upper-bound overhead that users set.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Leonard Foerster <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
include/linux/damon.h | 23 +++--
mm/damon/core.c | 214 +++++++++++++++++++++++++++++++++++++++++-
2 files changed, 227 insertions(+), 10 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 67db309ad61b..0bd5d6913a6c 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -12,6 +12,9 @@
#include <linux/time64.h>
#include <linux/types.h>

+/* Minimal region size. Every damon_region is aligned by this. */
+#define DAMON_MIN_REGION PAGE_SIZE
+
/**
* struct damon_addr_range - Represents an address region of [@start, @end).
* @start: Start address of the region (inclusive).
@@ -85,6 +88,8 @@ struct damon_ctx;
* prepared for the next access check.
* @check_accesses should check the accesses to each region that made after the
* last preparation and update the number of observed accesses of each region.
+ * It should also return max number of observed accesses that made as a result
+ * of its update. The value will be used for regions adjustment threshold.
* @reset_aggregated should reset the access monitoring results that aggregated
* by @check_accesses.
* @target_valid should check whether the target is still valid for the
@@ -95,7 +100,7 @@ struct damon_primitive {
void (*init)(struct damon_ctx *context);
void (*update)(struct damon_ctx *context);
void (*prepare_access_checks)(struct damon_ctx *context);
- void (*check_accesses)(struct damon_ctx *context);
+ unsigned int (*check_accesses)(struct damon_ctx *context);
void (*reset_aggregated)(struct damon_ctx *context);
bool (*target_valid)(void *target);
void (*cleanup)(struct damon_ctx *context);
@@ -172,7 +177,9 @@ struct damon_callback {
* @primitive: Set of monitoring primitives for given use cases.
* @callback: Set of callbacks for monitoring events notifications.
*
- * @region_targets: Head of monitoring targets (&damon_target) list.
+ * @min_nr_regions: The minimum number of adaptive monitoring regions.
+ * @max_nr_regions: The maximum number of adaptive monitoring regions.
+ * @adaptive_targets: Head of monitoring targets (&damon_target) list.
*/
struct damon_ctx {
unsigned long sample_interval;
@@ -191,7 +198,9 @@ struct damon_ctx {
struct damon_primitive primitive;
struct damon_callback callback;

- struct list_head region_targets;
+ unsigned long min_nr_regions;
+ unsigned long max_nr_regions;
+ struct list_head adaptive_targets;
};

#define damon_next_region(r) \
@@ -207,10 +216,10 @@ struct damon_ctx {
list_for_each_entry_safe(r, next, &t->regions_list, list)

#define damon_for_each_target(t, ctx) \
- list_for_each_entry(t, &(ctx)->region_targets, list)
+ list_for_each_entry(t, &(ctx)->adaptive_targets, list)

#define damon_for_each_target_safe(t, next, ctx) \
- list_for_each_entry_safe(t, next, &(ctx)->region_targets, list)
+ list_for_each_entry_safe(t, next, &(ctx)->adaptive_targets, list)

#ifdef CONFIG_DAMON

@@ -224,11 +233,13 @@ struct damon_target *damon_new_target(unsigned long id);
void damon_add_target(struct damon_ctx *ctx, struct damon_target *t);
void damon_free_target(struct damon_target *t);
void damon_destroy_target(struct damon_target *t);
+unsigned int damon_nr_regions(struct damon_target *t);

struct damon_ctx *damon_new_ctx(void);
void damon_destroy_ctx(struct damon_ctx *ctx);
int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
- unsigned long aggr_int, unsigned long primitive_upd_int);
+ unsigned long aggr_int, unsigned long primitive_upd_int,
+ unsigned long min_nr_reg, unsigned long max_nr_reg);

int damon_start(struct damon_ctx **ctxs, int nr_ctxs);
int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 94db494dcf70..b36b6bdd94e2 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -10,8 +10,12 @@
#include <linux/damon.h>
#include <linux/delay.h>
#include <linux/kthread.h>
+#include <linux/random.h>
#include <linux/slab.h>

+/* Get a random number in [l, r) */
+#define damon_rand(l, r) (l + prandom_u32_max(r - l))
+
static DEFINE_MUTEX(damon_lock);
static int nr_running_ctxs;

@@ -87,7 +91,7 @@ struct damon_target *damon_new_target(unsigned long id)

void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
{
- list_add_tail(&t->list, &ctx->region_targets);
+ list_add_tail(&t->list, &ctx->adaptive_targets);
}

static void damon_del_target(struct damon_target *t)
@@ -110,6 +114,17 @@ void damon_destroy_target(struct damon_target *t)
damon_free_target(t);
}

+unsigned int damon_nr_regions(struct damon_target *t)
+{
+ struct damon_region *r;
+ unsigned int nr_regions = 0;
+
+ damon_for_each_region(r, t)
+ nr_regions++;
+
+ return nr_regions;
+}
+
struct damon_ctx *damon_new_ctx(void)
{
struct damon_ctx *ctx;
@@ -127,7 +142,10 @@ struct damon_ctx *damon_new_ctx(void)

mutex_init(&ctx->kdamond_lock);

- INIT_LIST_HEAD(&ctx->region_targets);
+ ctx->min_nr_regions = 10;
+ ctx->max_nr_regions = 1000;
+
+ INIT_LIST_HEAD(&ctx->adaptive_targets);

return ctx;
}
@@ -157,6 +175,8 @@ void damon_destroy_ctx(struct damon_ctx *ctx)
* @sample_int: time interval between samplings
* @aggr_int: time interval between aggregations
* @primitive_upd_int: time interval between monitoring primitive updates
+ * @min_nr_reg: minimal number of regions
+ * @max_nr_reg: maximum number of regions
*
* This function should not be called while the kdamond is running.
* Every time interval is in micro-seconds.
@@ -164,15 +184,49 @@ void damon_destroy_ctx(struct damon_ctx *ctx)
* Return: 0 on success, negative error code otherwise.
*/
int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
- unsigned long aggr_int, unsigned long primitive_upd_int)
+ unsigned long aggr_int, unsigned long primitive_upd_int,
+ unsigned long min_nr_reg, unsigned long max_nr_reg)
{
+ if (min_nr_reg < 3) {
+ pr_err("min_nr_regions (%lu) must be at least 3\n",
+ min_nr_reg);
+ return -EINVAL;
+ }
+ if (min_nr_reg > max_nr_reg) {
+ pr_err("invalid nr_regions. min (%lu) > max (%lu)\n",
+ min_nr_reg, max_nr_reg);
+ return -EINVAL;
+ }
+
ctx->sample_interval = sample_int;
ctx->aggr_interval = aggr_int;
ctx->primitive_update_interval = primitive_upd_int;
+ ctx->min_nr_regions = min_nr_reg;
+ ctx->max_nr_regions = max_nr_reg;

return 0;
}

+/* Returns the size upper limit for each monitoring region */
+static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
+{
+ struct damon_target *t;
+ struct damon_region *r;
+ unsigned long sz = 0;
+
+ damon_for_each_target(t, ctx) {
+ damon_for_each_region(r, t)
+ sz += r->ar.end - r->ar.start;
+ }
+
+ if (ctx->min_nr_regions)
+ sz /= ctx->min_nr_regions;
+ if (sz < DAMON_MIN_REGION)
+ sz = DAMON_MIN_REGION;
+
+ return sz;
+}
+
static bool damon_kdamond_running(struct damon_ctx *ctx)
{
bool running;
@@ -339,6 +393,149 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
}
}

+#define sz_damon_region(r) (r->ar.end - r->ar.start)
+
+/*
+ * Merge two adjacent regions into one region
+ */
+static void damon_merge_two_regions(struct damon_region *l,
+ struct damon_region *r)
+{
+ unsigned long sz_l = sz_damon_region(l), sz_r = sz_damon_region(r);
+
+ l->nr_accesses = (l->nr_accesses * sz_l + r->nr_accesses * sz_r) /
+ (sz_l + sz_r);
+ l->ar.end = r->ar.end;
+ damon_destroy_region(r);
+}
+
+#define diff_of(a, b) (a > b ? a - b : b - a)
+
+/*
+ * Merge adjacent regions having similar access frequencies
+ *
+ * t target affected by this merge operation
+ * thres '->nr_accesses' diff threshold for the merge
+ * sz_limit size upper limit of each region
+ */
+static void damon_merge_regions_of(struct damon_target *t, unsigned int thres,
+ unsigned long sz_limit)
+{
+ struct damon_region *r, *prev = NULL, *next;
+
+ damon_for_each_region_safe(r, next, t) {
+ if (prev && prev->ar.end == r->ar.start &&
+ diff_of(prev->nr_accesses, r->nr_accesses) <= thres &&
+ sz_damon_region(prev) + sz_damon_region(r) <= sz_limit)
+ damon_merge_two_regions(prev, r);
+ else
+ prev = r;
+ }
+}
+
+/*
+ * Merge adjacent regions having similar access frequencies
+ *
+ * threshold '->nr_accesses' diff threshold for the merge
+ * sz_limit size upper limit of each region
+ *
+ * This function merges monitoring target regions which are adjacent and their
+ * access frequencies are similar. This is for minimizing the monitoring
+ * overhead under the dynamically changeable access pattern. If a merge was
+ * unnecessarily made, later 'kdamond_split_regions()' will revert it.
+ */
+static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold,
+ unsigned long sz_limit)
+{
+ struct damon_target *t;
+
+ damon_for_each_target(t, c)
+ damon_merge_regions_of(t, threshold, sz_limit);
+}
+
+/*
+ * Split a region in two
+ *
+ * r the region to be split
+ * sz_r size of the first sub-region that will be made
+ */
+static void damon_split_region_at(struct damon_ctx *ctx,
+ struct damon_region *r, unsigned long sz_r)
+{
+ struct damon_region *new;
+
+ new = damon_new_region(r->ar.start + sz_r, r->ar.end);
+ if (!new)
+ return;
+
+ r->ar.end = new->ar.start;
+
+ damon_insert_region(new, r, damon_next_region(r));
+}
+
+/* Split every region in the given target into 'nr_subs' regions */
+static void damon_split_regions_of(struct damon_ctx *ctx,
+ struct damon_target *t, int nr_subs)
+{
+ struct damon_region *r, *next;
+ unsigned long sz_region, sz_sub = 0;
+ int i;
+
+ damon_for_each_region_safe(r, next, t) {
+ sz_region = r->ar.end - r->ar.start;
+
+ for (i = 0; i < nr_subs - 1 &&
+ sz_region > 2 * DAMON_MIN_REGION; i++) {
+ /*
+ * Randomly select size of left sub-region to be at
+ * least 10 percent and at most 90% of original region
+ */
+ sz_sub = ALIGN_DOWN(damon_rand(1, 10) *
+ sz_region / 10, DAMON_MIN_REGION);
+ /* Do not allow blank region */
+ if (sz_sub == 0 || sz_sub >= sz_region)
+ continue;
+
+ damon_split_region_at(ctx, r, sz_sub);
+ sz_region = sz_sub;
+ }
+ }
+}
+
+/*
+ * Split every target region into randomly-sized small regions
+ *
+ * This function splits every target region into random-sized small regions if
+ * current total number of the regions is equal or smaller than half of the
+ * user-specified maximum number of regions. This is for maximizing the
+ * monitoring accuracy under the dynamically changeable access patterns. If a
+ * split was unnecessarily made, later 'kdamond_merge_regions()' will revert
+ * it.
+ */
+static void kdamond_split_regions(struct damon_ctx *ctx)
+{
+ struct damon_target *t;
+ unsigned int nr_regions = 0;
+ static unsigned int last_nr_regions;
+ int nr_subregions = 2;
+
+ damon_for_each_target(t, ctx)
+ nr_regions += damon_nr_regions(t);
+
+ if (nr_regions > ctx->max_nr_regions / 2)
+ return;
+
+ /* Maybe the middle of the region has different access frequency */
+ if (last_nr_regions == nr_regions &&
+ nr_regions < ctx->max_nr_regions / 3)
+ nr_subregions = 3;
+
+ damon_for_each_target(t, ctx)
+ damon_split_regions_of(ctx, t, nr_subregions);
+
+ last_nr_regions = nr_regions;
+}
+
/*
* Check whether it is time to check and apply the target monitoring regions
*
@@ -395,6 +592,8 @@ static int kdamond_fn(void *data)
struct damon_ctx *ctx = (struct damon_ctx *)data;
struct damon_target *t;
struct damon_region *r, *next;
+ unsigned int max_nr_accesses = 0;
+ unsigned long sz_limit = 0;

pr_info("kdamond (%d) starts\n", ctx->kdamond->pid);

@@ -403,6 +602,8 @@ static int kdamond_fn(void *data)
if (ctx->callback.before_start && ctx->callback.before_start(ctx))
set_kdamond_stop(ctx);

+ sz_limit = damon_region_sz_limit(ctx);
+
while (!kdamond_need_stop(ctx)) {
if (ctx->primitive.prepare_access_checks)
ctx->primitive.prepare_access_checks(ctx);
@@ -413,13 +614,17 @@ static int kdamond_fn(void *data)
usleep_range(ctx->sample_interval, ctx->sample_interval + 1);

if (ctx->primitive.check_accesses)
- ctx->primitive.check_accesses(ctx);
+ max_nr_accesses = ctx->primitive.check_accesses(ctx);

if (kdamond_aggregate_interval_passed(ctx)) {
+ kdamond_merge_regions(ctx,
+ max_nr_accesses / 10,
+ sz_limit);
if (ctx->callback.after_aggregation &&
ctx->callback.after_aggregation(ctx))
set_kdamond_stop(ctx);
kdamond_reset_aggregated(ctx);
+ kdamond_split_regions(ctx);
if (ctx->primitive.reset_aggregated)
ctx->primitive.reset_aggregated(ctx);
}
@@ -427,6 +632,7 @@ static int kdamond_fn(void *data)
if (kdamond_need_update_primitive(ctx)) {
if (ctx->primitive.update)
ctx->primitive.update(ctx);
+ sz_limit = damon_region_sz_limit(ctx);
}
}
damon_for_each_target(t, ctx) {
--
2.17.1

2021-06-21 08:33:37

by SeongJae Park

Subject: [PATCH v31 13/13] MAINTAINERS: Update for DAMON

From: SeongJae Park <[email protected]>

This commit updates MAINTAINERS file for DAMON related files.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Markus Boehme <[email protected]>
---
MAINTAINERS | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index dccbb23109a6..609bc9858748 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5095,6 +5095,18 @@ F: net/ax25/ax25_out.c
F: net/ax25/ax25_timer.c
F: net/ax25/sysctl_net_ax25.c

+DATA ACCESS MONITOR
+M: SeongJae Park <[email protected]>
+L: [email protected]
+S: Maintained
+F: Documentation/admin-guide/mm/damon/*
+F: Documentation/vm/damon/*
+F: include/linux/damon.h
+F: include/trace/events/damon.h
+F: mm/damon/*
+F: tools/damon/*
+F: tools/testing/selftests/damon/*
+
DAVICOM FAST ETHERNET (DMFE) NETWORK DRIVER
L: [email protected]
S: Orphan
--
2.17.1

2021-06-21 08:33:45

by SeongJae Park

Subject: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

From: SeongJae Park <[email protected]>

This commit introduces a reference implementation of the address space
specific low level primitives for the virtual address space, so that
users of DAMON can easily monitor the data accesses on virtual address
spaces of specific processes by simply configuring the implementation to
be used by DAMON.

The low level primitives for the fundamental access monitoring are
defined in two parts:

1. Identification of the monitoring target address range for the address
space.
2. Access check of specific address range in the target space.

The reference implementation for the virtual address space does the
works as below.

PTE Accessed-bit Based Access Check
-----------------------------------

The implementation uses PTE Accessed-bit for basic access checks. That
is, it clears the bit for the next sampling target page and checks
whether it is set again after one sampling period. This could disturb
the reclaim logic. DAMON uses ``PG_idle`` and ``PG_young`` page flags
to solve the conflict, as Idle page tracking does.

VMA-based Target Address Range Construction
-------------------------------------------

Only small parts in the super-huge virtual address space of the
processes are mapped to physical memory and accessed. Thus, tracking
the unmapped address regions is just wasteful. However, because DAMON
can deal with some level of noise using the adaptive regions adjustment
mechanism, tracking every mapping is not strictly required but could
even incur a high overhead in some cases. That said, too huge unmapped
areas inside the monitoring target should be removed to not take the
time for the adaptive mechanism.

For the reason, this implementation converts the complex mappings to
three distinct regions that cover every mapped area of the address
space. Also, the two gaps between the three regions are the two biggest
unmapped areas in the given address space. The two biggest unmapped
areas would be the gap between the heap and the uppermost mmap()-ed
region, and the gap between the lowermost mmap()-ed region and the stack
in most of the cases. Because these gaps are exceptionally huge in
usual address spaces, excluding these will be sufficient to make a
reasonable trade-off. Below shows this in detail::

<heap>
<BIG UNMAPPED REGION 1>
<uppermost mmap()-ed region>
(small mmap()-ed regions and munmap()-ed regions)
<lowermost mmap()-ed region>
<BIG UNMAPPED REGION 2>
<stack>

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Leonard Foerster <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
include/linux/damon.h | 13 +
mm/damon/Kconfig | 9 +
mm/damon/Makefile | 1 +
mm/damon/vaddr.c | 616 ++++++++++++++++++++++++++++++++++++++++++
4 files changed, 639 insertions(+)
create mode 100644 mm/damon/vaddr.c

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 0bd5d6913a6c..72cf5ebd35fe 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -246,4 +246,17 @@ int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);

#endif /* CONFIG_DAMON */

+#ifdef CONFIG_DAMON_VADDR
+
+/* Monitoring primitives for virtual memory address spaces */
+void damon_va_init(struct damon_ctx *ctx);
+void damon_va_update(struct damon_ctx *ctx);
+void damon_va_prepare_access_checks(struct damon_ctx *ctx);
+unsigned int damon_va_check_accesses(struct damon_ctx *ctx);
+bool damon_va_target_valid(void *t);
+void damon_va_cleanup(struct damon_ctx *ctx);
+void damon_va_set_primitives(struct damon_ctx *ctx);
+
+#endif /* CONFIG_DAMON_VADDR */
+
#endif /* _DAMON_H */
diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
index d00e99ac1a15..8ae080c52950 100644
--- a/mm/damon/Kconfig
+++ b/mm/damon/Kconfig
@@ -12,4 +12,13 @@ config DAMON
See https://damonitor.github.io/doc/html/latest-damon/index.html for
more information.

+config DAMON_VADDR
+ bool "Data access monitoring primitives for virtual address spaces"
+ depends on DAMON && MMU
+ select PAGE_EXTENSION if !64BIT
+ select PAGE_IDLE_FLAG
+ help
+ This builds the default data access monitoring primitives for DAMON
+ that works for virtual address spaces.
+
endmenu
diff --git a/mm/damon/Makefile b/mm/damon/Makefile
index 4fd2edb4becf..6ebbd08aed67 100644
--- a/mm/damon/Makefile
+++ b/mm/damon/Makefile
@@ -1,3 +1,4 @@
# SPDX-License-Identifier: GPL-2.0

obj-$(CONFIG_DAMON) := core.o
+obj-$(CONFIG_DAMON_VADDR) += vaddr.o
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
new file mode 100644
index 000000000000..3bc9dc9f0656
--- /dev/null
+++ b/mm/damon/vaddr.c
@@ -0,0 +1,616 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DAMON Primitives for Virtual Address Spaces
+ *
+ * Author: SeongJae Park <[email protected]>
+ */
+
+#define pr_fmt(fmt) "damon-va: " fmt
+
+#include <linux/damon.h>
+#include <linux/mm.h>
+#include <linux/mmu_notifier.h>
+#include <linux/page_idle.h>
+#include <linux/random.h>
+#include <linux/sched/mm.h>
+#include <linux/slab.h>
+
+/* Get a random number in [l, r) */
+#define damon_rand(l, r) (l + prandom_u32_max(r - l))
+
+/*
+ * 't->id' should be the pointer to the relevant 'struct pid' having reference
+ * count. Caller must put the returned task, unless it is NULL.
+ */
+#define damon_get_task_struct(t) \
+ (get_pid_task((struct pid *)t->id, PIDTYPE_PID))
+
+/*
+ * Get the mm_struct of the given target
+ *
+ * Caller _must_ put the mm_struct after use, unless it is NULL.
+ *
+ * Returns the mm_struct of the target on success, NULL on failure
+ */
+static struct mm_struct *damon_get_mm(struct damon_target *t)
+{
+ struct task_struct *task;
+ struct mm_struct *mm;
+
+ task = damon_get_task_struct(t);
+ if (!task)
+ return NULL;
+
+ mm = get_task_mm(task);
+ put_task_struct(task);
+ return mm;
+}
+
+/*
+ * Functions for the initial monitoring target regions construction
+ */
+
+/*
+ * Size-evenly split a region into 'nr_pieces' small regions
+ *
+ * Returns 0 on success, or negative error code otherwise.
+ */
+static int damon_va_evenly_split_region(struct damon_ctx *ctx,
+ struct damon_region *r, unsigned int nr_pieces)
+{
+ unsigned long sz_orig, sz_piece, orig_end;
+ struct damon_region *n = NULL, *next;
+ unsigned long start;
+
+ if (!r || !nr_pieces)
+ return -EINVAL;
+
+ orig_end = r->ar.end;
+ sz_orig = r->ar.end - r->ar.start;
+ sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);
+
+ if (!sz_piece)
+ return -EINVAL;
+
+ r->ar.end = r->ar.start + sz_piece;
+ next = damon_next_region(r);
+ for (start = r->ar.end; start + sz_piece <= orig_end;
+ start += sz_piece) {
+ n = damon_new_region(start, start + sz_piece);
+ if (!n)
+ return -ENOMEM;
+ damon_insert_region(n, r, next);
+ r = n;
+ }
+ /* complement last region for possible rounding error */
+ if (n)
+ n->ar.end = orig_end;
+
+ return 0;
+}
+
+static unsigned long sz_range(struct damon_addr_range *r)
+{
+ return r->end - r->start;
+}
+
+static void swap_ranges(struct damon_addr_range *r1,
+ struct damon_addr_range *r2)
+{
+ struct damon_addr_range tmp;
+
+ tmp = *r1;
+ *r1 = *r2;
+ *r2 = tmp;
+}
+
+/*
+ * Find three regions separated by two biggest unmapped regions
+ *
+ * vma the head vma of the target address space
+ * regions an array of three address ranges that results will be saved
+ *
+ * This function receives an address space and finds three regions in it which
+ * separated by the two biggest unmapped regions in the space. Please refer to
+ * below comments of '__damon_va_init_regions()' function to know why this is
+ * necessary.
+ *
+ * Returns 0 if success, or negative error code otherwise.
+ */
+static int __damon_va_three_regions(struct vm_area_struct *vma,
+ struct damon_addr_range regions[3])
+{
+ struct damon_addr_range gap = {0}, first_gap = {0}, second_gap = {0};
+ struct vm_area_struct *last_vma = NULL;
+ unsigned long start = 0;
+ struct rb_root rbroot;
+
+ /* Find two biggest gaps so that first_gap > second_gap > others */
+ for (; vma; vma = vma->vm_next) {
+ if (!last_vma) {
+ start = vma->vm_start;
+ goto next;
+ }
+
+ if (vma->rb_subtree_gap <= sz_range(&second_gap)) {
+ rbroot.rb_node = &vma->vm_rb;
+ vma = rb_entry(rb_last(&rbroot),
+ struct vm_area_struct, vm_rb);
+ goto next;
+ }
+
+ gap.start = last_vma->vm_end;
+ gap.end = vma->vm_start;
+ if (sz_range(&gap) > sz_range(&second_gap)) {
+ swap_ranges(&gap, &second_gap);
+ if (sz_range(&second_gap) > sz_range(&first_gap))
+ swap_ranges(&second_gap, &first_gap);
+ }
+next:
+ last_vma = vma;
+ }
+
+ if (!sz_range(&second_gap) || !sz_range(&first_gap))
+ return -EINVAL;
+
+ /* Sort the two biggest gaps by address */
+ if (first_gap.start > second_gap.start)
+ swap_ranges(&first_gap, &second_gap);
+
+ /* Store the result */
+ regions[0].start = ALIGN(start, DAMON_MIN_REGION);
+ regions[0].end = ALIGN(first_gap.start, DAMON_MIN_REGION);
+ regions[1].start = ALIGN(first_gap.end, DAMON_MIN_REGION);
+ regions[1].end = ALIGN(second_gap.start, DAMON_MIN_REGION);
+ regions[2].start = ALIGN(second_gap.end, DAMON_MIN_REGION);
+ regions[2].end = ALIGN(last_vma->vm_end, DAMON_MIN_REGION);
+
+ return 0;
+}
+
+/*
+ * Get the three regions in the given target (task)
+ *
+ * Returns 0 on success, negative error code otherwise.
+ */
+static int damon_va_three_regions(struct damon_target *t,
+ struct damon_addr_range regions[3])
+{
+ struct mm_struct *mm;
+ int rc;
+
+ mm = damon_get_mm(t);
+ if (!mm)
+ return -EINVAL;
+
+ mmap_read_lock(mm);
+ rc = __damon_va_three_regions(mm->mmap, regions);
+ mmap_read_unlock(mm);
+
+ mmput(mm);
+ return rc;
+}
+
+/*
+ * Initialize the monitoring target regions for the given target (task)
+ *
+ * t the given target
+ *
+ * Because only a number of small portions of the entire address space
+ * is actually mapped to the memory and accessed, monitoring the unmapped
+ * regions is wasteful. That said, because we can deal with small noises,
+ * tracking every mapping is not strictly required but could even incur a high
+ * overhead if the mapping frequently changes or the number of mappings is
+ * high. The adaptive regions adjustment mechanism will further help to deal
+ * with the noise by simply identifying the unmapped areas as a region that
+ * has no access. Moreover, applying the real mappings that would have many
+ * unmapped areas inside will make the adaptive mechanism quite complex. That
+ * said, too huge unmapped areas inside the monitoring target should be removed
+ * to not take the time for the adaptive mechanism.
+ *
+ * For the reason, we convert the complex mappings to three distinct regions
+ * that cover every mapped area of the address space. Also the two gaps
+ * between the three regions are the two biggest unmapped areas in the given
+ * address space. In detail, this function first identifies the start and the
+ * end of the mappings and the two biggest unmapped areas of the address space.
+ * Then, it constructs the three regions as below:
+ *
+ * [mappings[0]->start, big_two_unmapped_areas[0]->start)
+ * [big_two_unmapped_areas[0]->end, big_two_unmapped_areas[1]->start)
+ * [big_two_unmapped_areas[1]->end, mappings[nr_mappings - 1]->end)
+ *
+ * As usual memory map of processes is as below, the gap between the heap and
+ * the uppermost mmap()-ed region, and the gap between the lowermost mmap()-ed
+ * region and the stack will be two biggest unmapped regions. Because these
+ * gaps are exceptionally huge areas in usual address space, excluding these
+ * two biggest unmapped regions will be sufficient to make a trade-off.
+ *
+ * <heap>
+ * <BIG UNMAPPED REGION 1>
+ * <uppermost mmap()-ed region>
+ * (other mmap()-ed regions and small unmapped regions)
+ * <lowermost mmap()-ed region>
+ * <BIG UNMAPPED REGION 2>
+ * <stack>
+ */
+static void __damon_va_init_regions(struct damon_ctx *c,
+ struct damon_target *t)
+{
+ struct damon_region *r;
+ struct damon_addr_range regions[3];
+ unsigned long sz = 0, nr_pieces;
+ int i;
+
+ if (damon_va_three_regions(t, regions)) {
+ pr_err("Failed to get three regions of target %lu\n", t->id);
+ return;
+ }
+
+ for (i = 0; i < 3; i++)
+ sz += regions[i].end - regions[i].start;
+ if (c->min_nr_regions)
+ sz /= c->min_nr_regions;
+ if (sz < DAMON_MIN_REGION)
+ sz = DAMON_MIN_REGION;
+
+ /* Set the initial three regions of the target */
+ for (i = 0; i < 3; i++) {
+ r = damon_new_region(regions[i].start, regions[i].end);
+ if (!r) {
+ pr_err("%d'th init region creation failed\n", i);
+ return;
+ }
+ damon_add_region(r, t);
+
+ nr_pieces = (regions[i].end - regions[i].start) / sz;
+ damon_va_evenly_split_region(c, r, nr_pieces);
+ }
+}
+
+/* Initialize '->regions_list' of every target (task) */
+void damon_va_init(struct damon_ctx *ctx)
+{
+ struct damon_target *t;
+
+ damon_for_each_target(t, ctx) {
+ /* the user may set the target regions as they want */
+ if (!damon_nr_regions(t))
+ __damon_va_init_regions(ctx, t);
+ }
+}
+
+/*
+ * Functions for the dynamic monitoring target regions update
+ */
+
+/*
+ * Check whether a region is intersecting an address range
+ *
+ * Returns true if it is.
+ */
+static bool damon_intersect(struct damon_region *r, struct damon_addr_range *re)
+{
+ return !(r->ar.end <= re->start || re->end <= r->ar.start);
+}
+
+/*
+ * Update damon regions for the three big regions of the given target
+ *
+ * t the given target
+ * bregions the three big regions of the target
+ */
+static void damon_va_apply_three_regions(struct damon_ctx *ctx,
+ struct damon_target *t, struct damon_addr_range bregions[3])
+{
+ struct damon_region *r, *next;
+ unsigned int i = 0;
+
+ /* Remove regions which are not in the three big regions now */
+ damon_for_each_region_safe(r, next, t) {
+ for (i = 0; i < 3; i++) {
+ if (damon_intersect(r, &bregions[i]))
+ break;
+ }
+ if (i == 3)
+ damon_destroy_region(r);
+ }
+
+ /* Adjust intersecting regions to fit with the three big regions */
+ for (i = 0; i < 3; i++) {
+ struct damon_region *first = NULL, *last;
+ struct damon_region *newr;
+ struct damon_addr_range *br;
+
+ br = &bregions[i];
+ /* Get the first and last regions which intersects with br */
+ damon_for_each_region(r, t) {
+ if (damon_intersect(r, br)) {
+ if (!first)
+ first = r;
+ last = r;
+ }
+ if (r->ar.start >= br->end)
+ break;
+ }
+ if (!first) {
+ /* no damon_region intersects with this big region */
+ newr = damon_new_region(
+ ALIGN_DOWN(br->start,
+ DAMON_MIN_REGION),
+ ALIGN(br->end, DAMON_MIN_REGION));
+ if (!newr)
+ continue;
+ damon_insert_region(newr, damon_prev_region(r), r);
+ } else {
+ first->ar.start = ALIGN_DOWN(br->start,
+ DAMON_MIN_REGION);
+ last->ar.end = ALIGN(br->end, DAMON_MIN_REGION);
+ }
+ }
+}
+
+/*
+ * Update regions for current memory mappings
+ */
+void damon_va_update(struct damon_ctx *ctx)
+{
+ struct damon_addr_range three_regions[3];
+ struct damon_target *t;
+
+ damon_for_each_target(t, ctx) {
+ if (damon_va_three_regions(t, three_regions))
+ continue;
+ damon_va_apply_three_regions(ctx, t, three_regions);
+ }
+}
+
+/*
+ * Get an online page for a pfn if it's in the LRU list. Otherwise, returns
+ * NULL.
+ *
+ * The body of this function is stolen from the 'page_idle_get_page()'. We
+ * steal rather than reuse it because the code is quite simple.
+ */
+static struct page *damon_get_page(unsigned long pfn)
+{
+ struct page *page = pfn_to_online_page(pfn);
+
+ if (!page || !PageLRU(page) || !get_page_unless_zero(page))
+ return NULL;
+
+ if (unlikely(!PageLRU(page))) {
+ put_page(page);
+ page = NULL;
+ }
+ return page;
+}
+
+static void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm,
+ unsigned long addr)
+{
+ bool referenced = false;
+ struct page *page = damon_get_page(pte_pfn(*pte));
+
+ if (!page)
+ return;
+
+ if (pte_young(*pte)) {
+ referenced = true;
+ *pte = pte_mkold(*pte);
+ }
+
+#ifdef CONFIG_MMU_NOTIFIER
+ if (mmu_notifier_clear_young(mm, addr, addr + PAGE_SIZE))
+ referenced = true;
+#endif /* CONFIG_MMU_NOTIFIER */
+
+ if (referenced)
+ set_page_young(page);
+
+ set_page_idle(page);
+ put_page(page);
+}
+
+static void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm,
+ unsigned long addr)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ bool referenced = false;
+ struct page *page = damon_get_page(pmd_pfn(*pmd));
+
+ if (!page)
+ return;
+
+ if (pmd_young(*pmd)) {
+ referenced = true;
+ *pmd = pmd_mkold(*pmd);
+ }
+
+#ifdef CONFIG_MMU_NOTIFIER
+ if (mmu_notifier_clear_young(mm, addr,
+ addr + ((1UL) << HPAGE_PMD_SHIFT)))
+ referenced = true;
+#endif /* CONFIG_MMU_NOTIFIER */
+
+ if (referenced)
+ set_page_young(page);
+
+ set_page_idle(page);
+ put_page(page);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+}
+
+static void damon_va_mkold(struct mm_struct *mm, unsigned long addr)
+{
+ pte_t *pte = NULL;
+ pmd_t *pmd = NULL;
+ spinlock_t *ptl;
+
+ if (follow_invalidate_pte(mm, addr, NULL, &pte, &pmd, &ptl))
+ return;
+
+ if (pte) {
+ damon_ptep_mkold(pte, mm, addr);
+ pte_unmap_unlock(pte, ptl);
+ } else {
+ damon_pmdp_mkold(pmd, mm, addr);
+ spin_unlock(ptl);
+ }
+}
+
+/*
+ * Functions for the access checking of the regions
+ */
+
+static void damon_va_prepare_access_check(struct damon_ctx *ctx,
+ struct mm_struct *mm, struct damon_region *r)
+{
+ r->sampling_addr = damon_rand(r->ar.start, r->ar.end);
+
+ damon_va_mkold(mm, r->sampling_addr);
+}
+
+void damon_va_prepare_access_checks(struct damon_ctx *ctx)
+{
+ struct damon_target *t;
+ struct mm_struct *mm;
+ struct damon_region *r;
+
+ damon_for_each_target(t, ctx) {
+ mm = damon_get_mm(t);
+ if (!mm)
+ continue;
+ damon_for_each_region(r, t)
+ damon_va_prepare_access_check(ctx, mm, r);
+ mmput(mm);
+ }
+}
+
+static bool damon_va_young(struct mm_struct *mm, unsigned long addr,
+ unsigned long *page_sz)
+{
+ pte_t *pte = NULL;
+ pmd_t *pmd = NULL;
+ spinlock_t *ptl;
+ struct page *page;
+ bool young = false;
+
+ if (follow_invalidate_pte(mm, addr, NULL, &pte, &pmd, &ptl))
+ return false;
+
+ *page_sz = PAGE_SIZE;
+ if (pte) {
+ page = damon_get_page(pte_pfn(*pte));
+ if (page && (pte_young(*pte) || !page_is_idle(page) ||
+ mmu_notifier_test_young(mm, addr)))
+ young = true;
+ if (page)
+ put_page(page);
+ pte_unmap_unlock(pte, ptl);
+ return young;
+ }
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ page = damon_get_page(pmd_pfn(*pmd));
+ if (page && (pmd_young(*pmd) || !page_is_idle(page) ||
+ mmu_notifier_test_young(mm, addr)))
+ young = true;
+ if (page)
+ put_page(page);
+
+ spin_unlock(ptl);
+ *page_sz = ((1UL) << HPAGE_PMD_SHIFT);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+ return young;
+}
+
+/*
+ * Check whether the region was accessed after the last preparation
+ *
+ * mm 'mm_struct' for the given virtual address space
+ * r the region to be checked
+ */
+static void damon_va_check_access(struct damon_ctx *ctx,
+ struct mm_struct *mm, struct damon_region *r)
+{
+ static struct mm_struct *last_mm;
+ static unsigned long last_addr;
+ static unsigned long last_page_sz = PAGE_SIZE;
+ static bool last_accessed;
+
+ /* If the region is in the last checked page, reuse the result */
+ if (mm == last_mm && (ALIGN_DOWN(last_addr, last_page_sz) ==
+ ALIGN_DOWN(r->sampling_addr, last_page_sz))) {
+ if (last_accessed)
+ r->nr_accesses++;
+ return;
+ }
+
+ last_accessed = damon_va_young(mm, r->sampling_addr, &last_page_sz);
+ if (last_accessed)
+ r->nr_accesses++;
+
+ last_mm = mm;
+ last_addr = r->sampling_addr;
+}
+
+unsigned int damon_va_check_accesses(struct damon_ctx *ctx)
+{
+ struct damon_target *t;
+ struct mm_struct *mm;
+ struct damon_region *r;
+ unsigned int max_nr_accesses = 0;
+
+ damon_for_each_target(t, ctx) {
+ mm = damon_get_mm(t);
+ if (!mm)
+ continue;
+ damon_for_each_region(r, t) {
+ damon_va_check_access(ctx, mm, r);
+ max_nr_accesses = max(r->nr_accesses, max_nr_accesses);
+ }
+ mmput(mm);
+ }
+
+ return max_nr_accesses;
+}
+
+/*
+ * Functions for the target validity check and cleanup
+ */
+
+bool damon_va_target_valid(void *target)
+{
+ struct damon_target *t = target;
+ struct task_struct *task;
+
+ task = damon_get_task_struct(t);
+ if (task) {
+ put_task_struct(task);
+ return true;
+ }
+
+ return false;
+}
+
+void damon_va_cleanup(struct damon_ctx *ctx)
+{
+ struct damon_target *t, *next;
+
+ damon_for_each_target_safe(t, next, ctx) {
+ put_pid((struct pid *)t->id);
+ damon_destroy_target(t);
+ }
+}
+
+void damon_va_set_primitives(struct damon_ctx *ctx)
+{
+ ctx->primitive.init = damon_va_init;
+ ctx->primitive.update = damon_va_update;
+ ctx->primitive.prepare_access_checks = damon_va_prepare_access_checks;
+ ctx->primitive.check_accesses = damon_va_check_accesses;
+ ctx->primitive.reset_aggregated = NULL;
+ ctx->primitive.target_valid = damon_va_target_valid;
+ ctx->primitive.cleanup = damon_va_cleanup;
+}
--
2.17.1

2021-06-21 08:34:04

by SeongJae Park

Subject: [PATCH v31 09/13] mm/damon/dbgfs: Support multiple contexts

From: SeongJae Park <[email protected]>

In some use cases, users would want to run multiple monitoring context.
For example, if a user wants a high precision monitoring and dedicating
multiple CPUs for the job is ok, because DAMON creates one monitoring
thread per one context, the user can split the monitoring target regions
into multiple small regions and create one context for each region. Or,
someone might want to simultaneously monitor different address spaces,
e.g., both virtual address space and physical address space.

The DAMON's API allows such usage, but 'damon-dbgfs' does not.
Therefore, only kernel space DAMON users can do multiple contexts
monitoring.

This commit allows the user space DAMON users to use multiple contexts
monitoring by introducing two new 'damon-dbgfs' debugfs files,
'mk_context' and 'rm_context'. Users can create a new monitoring
context by writing the desired name of the new context to 'mk_context'.
Then, a new directory with the name and having the files for setting of
the context ('attrs', 'target_ids' and 'record') will be created under
the debugfs directory. Writing the name of the context to remove to
'rm_context' will remove the related context and directory.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Fernand Sieber <[email protected]>
---
mm/damon/dbgfs.c | 197 ++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 195 insertions(+), 2 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 524362f8c628..07bc03f7f34d 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -18,6 +18,7 @@
static struct damon_ctx **dbgfs_ctxs;
static int dbgfs_nr_ctxs;
static struct dentry **dbgfs_dirs;
+static DEFINE_MUTEX(damon_dbgfs_lock);

/*
* Returns non-empty string on success, negative error code otherwise.
@@ -314,6 +315,186 @@ static struct damon_ctx *dbgfs_new_ctx(void)
return ctx;
}

+static void dbgfs_destroy_ctx(struct damon_ctx *ctx)
+{
+ damon_destroy_ctx(ctx);
+}
+
+/*
+ * Make a context of @name and create a debugfs directory for it.
+ *
+ * This function should be called while holding damon_dbgfs_lock.
+ *
+ * Returns 0 on success, negative error code otherwise.
+ */
+static int dbgfs_mk_context(char *name)
+{
+ struct dentry *root, **new_dirs, *new_dir;
+ struct damon_ctx **new_ctxs, *new_ctx;
+
+ if (damon_nr_running_ctxs())
+ return -EBUSY;
+
+ new_ctxs = krealloc(dbgfs_ctxs, sizeof(*dbgfs_ctxs) *
+ (dbgfs_nr_ctxs + 1), GFP_KERNEL);
+ if (!new_ctxs)
+ return -ENOMEM;
+ dbgfs_ctxs = new_ctxs;
+
+ new_dirs = krealloc(dbgfs_dirs, sizeof(*dbgfs_dirs) *
+ (dbgfs_nr_ctxs + 1), GFP_KERNEL);
+ if (!new_dirs)
+ return -ENOMEM;
+ dbgfs_dirs = new_dirs;
+
+ root = dbgfs_dirs[0];
+ if (!root)
+ return -ENOENT;
+
+ new_dir = debugfs_create_dir(name, root);
+ dbgfs_dirs[dbgfs_nr_ctxs] = new_dir;
+
+ new_ctx = dbgfs_new_ctx();
+ if (!new_ctx) {
+ debugfs_remove(new_dir);
+ dbgfs_dirs[dbgfs_nr_ctxs] = NULL;
+ return -ENOMEM;
+ }
+
+ dbgfs_ctxs[dbgfs_nr_ctxs] = new_ctx;
+ dbgfs_fill_ctx_dir(dbgfs_dirs[dbgfs_nr_ctxs],
+ dbgfs_ctxs[dbgfs_nr_ctxs]);
+ dbgfs_nr_ctxs++;
+
+ return 0;
+}
+
+static ssize_t dbgfs_mk_context_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ char *kbuf;
+ char *ctx_name;
+ ssize_t ret = count;
+ int err;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+ ctx_name = kmalloc(count + 1, GFP_KERNEL);
+ if (!ctx_name) {
+ kfree(kbuf);
+ return -ENOMEM;
+ }
+
+ /* Trim white space */
+ if (sscanf(kbuf, "%s", ctx_name) != 1) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ mutex_lock(&damon_dbgfs_lock);
+ err = dbgfs_mk_context(ctx_name);
+ if (err)
+ ret = err;
+ mutex_unlock(&damon_dbgfs_lock);
+
+out:
+ kfree(kbuf);
+ kfree(ctx_name);
+ return ret;
+}
+
+/*
+ * Remove a context of @name and its debugfs directory.
+ *
+ * This function should be called while holding damon_dbgfs_lock.
+ *
+ * Return 0 on success, negative error code otherwise.
+ */
+static int dbgfs_rm_context(char *name)
+{
+ struct dentry *root, *dir, **new_dirs;
+ struct damon_ctx **new_ctxs;
+ int i, j;
+
+ if (damon_nr_running_ctxs())
+ return -EBUSY;
+
+ root = dbgfs_dirs[0];
+ if (!root)
+ return -ENOENT;
+
+ dir = debugfs_lookup(name, root);
+ if (!dir)
+ return -ENOENT;
+
+ new_dirs = kmalloc_array(dbgfs_nr_ctxs - 1, sizeof(*dbgfs_dirs),
+ GFP_KERNEL);
+ if (!new_dirs)
+ return -ENOMEM;
+
+ new_ctxs = kmalloc_array(dbgfs_nr_ctxs - 1, sizeof(*dbgfs_ctxs),
+ GFP_KERNEL);
+ if (!new_ctxs) {
+ kfree(new_dirs);
+ return -ENOMEM;
+ }
+
+ for (i = 0, j = 0; i < dbgfs_nr_ctxs; i++) {
+ if (dbgfs_dirs[i] == dir) {
+ debugfs_remove(dbgfs_dirs[i]);
+ dbgfs_destroy_ctx(dbgfs_ctxs[i]);
+ continue;
+ }
+ new_dirs[j] = dbgfs_dirs[i];
+ new_ctxs[j++] = dbgfs_ctxs[i];
+ }
+
+ kfree(dbgfs_dirs);
+ kfree(dbgfs_ctxs);
+
+ dbgfs_dirs = new_dirs;
+ dbgfs_ctxs = new_ctxs;
+ dbgfs_nr_ctxs--;
+
+ return 0;
+}
+
+static ssize_t dbgfs_rm_context_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ char *kbuf;
+ ssize_t ret = count;
+ int err;
+ char *ctx_name;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+ ctx_name = kmalloc(count + 1, GFP_KERNEL);
+ if (!ctx_name) {
+ kfree(kbuf);
+ return -ENOMEM;
+ }
+
+ /* Trim white space */
+ if (sscanf(kbuf, "%s", ctx_name) != 1) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ mutex_lock(&damon_dbgfs_lock);
+ err = dbgfs_rm_context(ctx_name);
+ if (err)
+ ret = err;
+ mutex_unlock(&damon_dbgfs_lock);
+
+out:
+ kfree(kbuf);
+ kfree(ctx_name);
+ return ret;
+}
+
static ssize_t dbgfs_monitor_on_read(struct file *file,
char __user *buf, size_t count, loff_t *ppos)
{
@@ -356,6 +537,16 @@ static ssize_t dbgfs_monitor_on_write(struct file *file,
return ret;
}

+static const struct file_operations mk_contexts_fops = {
+ .owner = THIS_MODULE,
+ .write = dbgfs_mk_context_write,
+};
+
+static const struct file_operations rm_contexts_fops = {
+ .owner = THIS_MODULE,
+ .write = dbgfs_rm_context_write,
+};
+
static const struct file_operations monitor_on_fops = {
.owner = THIS_MODULE,
.read = dbgfs_monitor_on_read,
@@ -365,8 +556,10 @@ static const struct file_operations monitor_on_fops = {
static int __init __damon_dbgfs_init(void)
{
struct dentry *dbgfs_root;
- const char * const file_names[] = {"monitor_on"};
- const struct file_operations *fops[] = {&monitor_on_fops};
+ const char * const file_names[] = {"mk_contexts", "rm_contexts",
+ "monitor_on"};
+ const struct file_operations *fops[] = {&mk_contexts_fops,
+ &rm_contexts_fops, &monitor_on_fops};
int i;

dbgfs_root = debugfs_create_dir("damon", NULL);
--
2.17.1

2021-06-21 08:34:31

by SeongJae Park

Subject: [PATCH v31 12/13] mm/damon: Add user space selftests

From: SeongJae Park <[email protected]>

This commit adds a simple user space tests for DAMON. The tests are
using kselftest framework.

Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Markus Boehme <[email protected]>
---
tools/testing/selftests/damon/Makefile | 7 ++
.../selftests/damon/_chk_dependency.sh | 28 +++++++
.../testing/selftests/damon/debugfs_attrs.sh | 75 +++++++++++++++++++
3 files changed, 110 insertions(+)
create mode 100644 tools/testing/selftests/damon/Makefile
create mode 100644 tools/testing/selftests/damon/_chk_dependency.sh
create mode 100755 tools/testing/selftests/damon/debugfs_attrs.sh

diff --git a/tools/testing/selftests/damon/Makefile b/tools/testing/selftests/damon/Makefile
new file mode 100644
index 000000000000..8a3f2cd9fec0
--- /dev/null
+++ b/tools/testing/selftests/damon/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for damon selftests
+
+TEST_FILES = _chk_dependency.sh
+TEST_PROGS = debugfs_attrs.sh
+
+include ../lib.mk
diff --git a/tools/testing/selftests/damon/_chk_dependency.sh b/tools/testing/selftests/damon/_chk_dependency.sh
new file mode 100644
index 000000000000..0189db81550b
--- /dev/null
+++ b/tools/testing/selftests/damon/_chk_dependency.sh
@@ -0,0 +1,28 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+DBGFS=/sys/kernel/debug/damon
+
+if [ $EUID -ne 0 ];
+then
+ echo "Run as root"
+ exit $ksft_skip
+fi
+
+if [ ! -d "$DBGFS" ]
+then
+ echo "$DBGFS not found"
+ exit $ksft_skip
+fi
+
+for f in attrs target_ids monitor_on
+do
+ if [ ! -f "$DBGFS/$f" ]
+ then
+ echo "$f not found"
+ exit 1
+ fi
+done
diff --git a/tools/testing/selftests/damon/debugfs_attrs.sh b/tools/testing/selftests/damon/debugfs_attrs.sh
new file mode 100755
index 000000000000..bfabb19dc0d3
--- /dev/null
+++ b/tools/testing/selftests/damon/debugfs_attrs.sh
@@ -0,0 +1,75 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+test_write_result() {
+ file=$1
+ content=$2
+ orig_content=$3
+ expect_reason=$4
+ expected=$5
+
+ echo "$content" > "$file"
+ if [ $? -ne "$expected" ]
+ then
+ echo "writing $content to $file doesn't return $expected"
+ echo "expected because: $expect_reason"
+ echo "$orig_content" > "$file"
+ exit 1
+ fi
+}
+
+test_write_succ() {
+ test_write_result "$1" "$2" "$3" "$4" 0
+}
+
+test_write_fail() {
+ test_write_result "$1" "$2" "$3" "$4" 1
+}
+
+test_content() {
+ file=$1
+ orig_content=$2
+ expected=$3
+ expect_reason=$4
+
+ content=$(cat "$file")
+ if [ "$content" != "$expected" ]
+ then
+ echo "reading $file expected $expected but $content"
+ echo "expected because: $expect_reason"
+ echo "$orig_content" > "$file"
+ exit 1
+ fi
+}
+
+source ./_chk_dependency.sh
+
+# Test attrs file
+# ===============
+
+file="$DBGFS/attrs"
+orig_content=$(cat "$file")
+
+test_write_succ "$file" "1 2 3 4 5" "$orig_content" "valid input"
+test_write_fail "$file" "1 2 3 4" "$orig_content" "no enough fields"
+test_write_fail "$file" "1 2 3 5 4" "$orig_content" \
+ "min_nr_regions > max_nr_regions"
+test_content "$file" "$orig_content" "1 2 3 4 5" "successfully written"
+echo "$orig_content" > "$file"
+
+# Test target_ids file
+# ====================
+
+file="$DBGFS/target_ids"
+orig_content=$(cat "$file")
+
+test_write_succ "$file" "1 2 3 4" "$orig_content" "valid input"
+test_write_succ "$file" "1 2 abc 4" "$orig_content" "still valid input"
+test_content "$file" "$orig_content" "1 2" "non-integer was there"
+test_write_succ "$file" "abc 2 3" "$orig_content" "the file allows wrong input"
+test_content "$file" "$orig_content" "" "wrong input written"
+test_write_succ "$file" "" "$orig_content" "empty input"
+test_content "$file" "$orig_content" "" "empty input written"
+echo "$orig_content" > "$file"
+
+echo "PASS"
--
2.17.1

2021-06-22 15:00:39

by Shakeel Butt

Subject: Re: [PATCH v31 01/13] mm: Introduce Data Access MONitor (DAMON)

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> DAMON is a data access monitoring framework for the Linux kernel. The
> core mechanisms of DAMON make it
>
> - accurate (the monitoring output is useful enough for DRAM level
> performance-centric memory management; It might be inappropriate for
> CPU cache levels, though),
> - light-weight (the monitoring overhead is normally low enough to be
> applied online), and
> - scalable (the upper-bound of the overhead is in constant range
> regardless of the size of target workloads).
>
> Using this framework, hence, we can easily write efficient kernel space
> data access monitoring applications. For example, the kernel's memory
> management mechanisms can make advanced decisions using this.
> Experimental data access aware optimization works that incurring high
> access monitoring overhead could again be implemented on top of this.
>
> Due to its simple and flexible interface, providing user space interface
> would be also easy. Then, user space users who have some special
> workloads can write personalized applications for better understanding
> and optimizations of their workloads and systems.
>
> ===
>
> Nevertheless, this commit is defining and implementing only basic access
> check part without the overhead-accuracy handling core logic. The basic
> access check is as below.
>
> The output of DAMON says what memory regions are how frequently accessed
> for a given duration. The resolution of the access frequency is
> controlled by setting ``sampling interval`` and ``aggregation
> interval``. In detail, DAMON checks access to each page per ``sampling
> interval`` and aggregates the results. In other words, counts the
> number of the accesses to each region. After each ``aggregation
> interval`` passes, DAMON calls callback functions that previously
> registered by users so that users can read the aggregated results and
> then clears the results. This can be described in below simple
> pseudo-code::
>
> init()
> while monitoring_on:
> for page in monitoring_target:
> if accessed(page):
> nr_accesses[page] += 1
> if time() % aggregation_interval == 0:
> for callback in user_registered_callbacks:
> callback(monitoring_target, nr_accesses)
> for page in monitoring_target:
> nr_accesses[page] = 0
> if time() % update_interval == 0:

regions_update_interval?

> update()
> sleep(sampling interval)
>
> The target regions constructed at the beginning of the monitoring and
> updated after each ``regions_update_interval``, because the target
> regions could be dynamically changed (e.g., mmap() or memory hotplug).
> The monitoring overhead of this mechanism will arbitrarily increase as
> the size of the target workload grows.
>
> The basic monitoring primitives for actual access check and dynamic
> target regions construction aren't in the core part of DAMON. Instead,
> it allows users to implement their own primitives that are optimized for
> their use case and configure DAMON to use those. In other words, users
> cannot use current version of DAMON without some additional works.
>
> Following commits will implement the core mechanisms for the
> overhead-accuracy control and default primitives implementations.
>
> Signed-off-by: SeongJae Park <[email protected]>
> Reviewed-by: Leonard Foerster <[email protected]>
> Reviewed-by: Fernand Sieber <[email protected]>

Few nits below otherwise look good to me. You can add:

Acked-by: Shakeel Butt <[email protected]>

[...]
> +/*
> + * __damon_start() - Starts monitoring with given context.
> + * @ctx: monitoring context
> + *
> + * This function should be called while damon_lock is hold.
> + *
> + * Return: 0 on success, negative error code otherwise.
> + */
> +static int __damon_start(struct damon_ctx *ctx)
> +{
> + int err = -EBUSY;
> +
> + mutex_lock(&ctx->kdamond_lock);
> + if (!ctx->kdamond) {
> + err = 0;
> + ctx->kdamond_stop = false;
> + ctx->kdamond = kthread_create(kdamond_fn, ctx, "kdamond.%d",
> + nr_running_ctxs);
> + if (IS_ERR(ctx->kdamond))
> + err = PTR_ERR(ctx->kdamond);
> + else
> + wake_up_process(ctx->kdamond);

Nit: You can use kthread_run() here.

> + }
> + mutex_unlock(&ctx->kdamond_lock);
> +
> + return err;
> +}
> +
[...]
> +static int __damon_stop(struct damon_ctx *ctx)
> +{
> + mutex_lock(&ctx->kdamond_lock);
> + if (ctx->kdamond) {
> + ctx->kdamond_stop = true;
> + mutex_unlock(&ctx->kdamond_lock);
> + while (damon_kdamond_running(ctx))
> + usleep_range(ctx->sample_interval,
> + ctx->sample_interval * 2);

Any reason to not use kthread_stop() here?

2021-06-22 15:00:44

by Shakeel Butt

Subject: Re: [PATCH v31 02/13] mm/damon/core: Implement region-based sampling

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> To avoid the unbounded increase of the overhead, DAMON groups adjacent
> pages that are assumed to have the same access frequencies into a
> region. As long as the assumption (pages in a region have the same
> access frequencies) is kept, only one page in the region is required to
> be checked. Thus, for each ``sampling interval``,
>
> 1. the 'prepare_access_checks' primitive picks one page in each region,
> 2. waits for one ``sampling interval``,
> 3. checks whether the page is accessed meanwhile, and
> 4. increases the access count of the region if so.
>
> Therefore, the monitoring overhead is controllable by adjusting the
> number of regions. DAMON allows both the underlying primitives and user
> callbacks to adjust regions for the trade-off. In other words, this
> commit makes DAMON to use not only time-based sampling but also
> space-based sampling.
>
> This scheme, however, cannot preserve the quality of the output if the
> assumption is not guaranteed. Next commit will address this problem.
>
> Signed-off-by: SeongJae Park <[email protected]>
> Reviewed-by: Leonard Foerster <[email protected]>
> Reviewed-by: Fernand Sieber <[email protected]>

Acked-by: Shakeel Butt <[email protected]>

2021-06-22 15:02:38

by Shakeel Butt

Subject: Re: [PATCH v31 03/13] mm/damon: Adaptively adjust regions

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> Even somehow the initial monitoring target regions are well constructed
> to fulfill the assumption (pages in same region have similar access
> frequencies), the data access pattern can be dynamically changed. This
> will result in low monitoring quality. To keep the assumption as much
> as possible, DAMON adaptively merges and splits each region based on
> their access frequency.
>
> For each ``aggregation interval``, it compares the access frequencies of
> adjacent regions and merges those if the frequency difference is small.
> Then, after it reports and clears the aggregated access frequency of
> each region, it splits each region into two or three regions if the
> total number of regions will not exceed the user-specified maximum
> number of regions after the split.
>
> In this way, DAMON provides its best-effort quality and minimal overhead
> while keeping the upper-bound overhead that users set.
>
> Signed-off-by: SeongJae Park <[email protected]>
> Reviewed-by: Leonard Foerster <[email protected]>
> Reviewed-by: Fernand Sieber <[email protected]>
[...]
>
> +unsigned int damon_nr_regions(struct damon_target *t)
> +{
> + struct damon_region *r;
> + unsigned int nr_regions = 0;
> +
> + damon_for_each_region(r, t)
> + nr_regions++;

This bugs me everytime. Please just have nr_regions field in the
damon_target instead of traversing the list to count the number of
regions.

Other than that, it looks good to me.

2021-06-22 15:02:47

by Shakeel Butt

Subject: Re: [PATCH v31 06/13] mm/damon: Add a tracepoint

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> This commit adds a tracepoint for DAMON. It traces the monitoring
> results of each region for each aggregation interval. Using this, DAMON
> can easily integrated with tracepoints supporting tools such as perf.
>
> Signed-off-by: SeongJae Park <[email protected]>
> Reviewed-by: Leonard Foerster <[email protected]>
> Reviewed-by: Steven Rostedt (VMware) <[email protected]>
> Reviewed-by: Fernand Sieber <[email protected]>

Acked-by: Shakeel Butt <[email protected]>

2021-06-22 15:03:15

by Shakeel Butt

Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> This commit introduces a reference implementation of the address space
> specific low level primitives for the virtual address space, so that
> users of DAMON can easily monitor the data accesses on virtual address
> spaces of specific processes by simply configuring the implementation to
> be used by DAMON.
>
> The low level primitives for the fundamental access monitoring are
> defined in two parts:
>
> 1. Identification of the monitoring target address range for the address
> space.
> 2. Access check of specific address range in the target space.
>
> The reference implementation for the virtual address space does the
> works as below.
>
> PTE Accessed-bit Based Access Check
> -----------------------------------
>
> The implementation uses PTE Accessed-bit for basic access checks. That
> is, it clears the bit for the next sampling target page and checks
> whether it is set again after one sampling period. This could disturb
> the reclaim logic. DAMON uses ``PG_idle`` and ``PG_young`` page flags
> to solve the conflict, as Idle page tracking does.
>
> VMA-based Target Address Range Construction
> -------------------------------------------
>
> Only small parts in the super-huge virtual address space of the
> processes are mapped to physical memory and accessed. Thus, tracking
> the unmapped address regions is just wasteful. However, because DAMON
> can deal with some level of noise using the adaptive regions adjustment
> mechanism, tracking every mapping is not strictly required but could
> even incur a high overhead in some cases. That said, too huge unmapped
> areas inside the monitoring target should be removed to not take the
> time for the adaptive mechanism.
>
> For the reason, this implementation converts the complex mappings to
> three distinct regions that cover every mapped area of the address
> space. Also, the two gaps between the three regions are the two biggest
> unmapped areas in the given address space. The two biggest unmapped
> areas would be the gap between the heap and the uppermost mmap()-ed
> region, and the gap between the lowermost mmap()-ed region and the stack
> in most of the cases. Because these gaps are exceptionally huge in
> usual address spaces, excluding these will be sufficient to make a
> reasonable trade-off. Below shows this in detail::
>
> <heap>
> <BIG UNMAPPED REGION 1>
> <uppermost mmap()-ed region>
> (small mmap()-ed regions and munmap()-ed regions)
> <lowermost mmap()-ed region>
> <BIG UNMAPPED REGION 2>
> <stack>
>
> Signed-off-by: SeongJae Park <[email protected]>
> Reviewed-by: Leonard Foerster <[email protected]>
> Reviewed-by: Fernand Sieber <[email protected]>

Couple of nits below and one concern on the default value of
primitive_update_interval of virtual address space primitive.
Otherwise looks good to me.

[...]

> +
> +/*
> + * Size-evenly split a region into 'nr_pieces' small regions
> + *
> + * Returns 0 on success, or negative error code otherwise.
> + */
> +static int damon_va_evenly_split_region(struct damon_ctx *ctx,

I don't see ctx being used in this function.

> + struct damon_region *r, unsigned int nr_pieces)
> +{
> + unsigned long sz_orig, sz_piece, orig_end;
> + struct damon_region *n = NULL, *next;
> + unsigned long start;
> +
> + if (!r || !nr_pieces)
> + return -EINVAL;
> +
> + orig_end = r->ar.end;
> + sz_orig = r->ar.end - r->ar.start;
> + sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);
> +
> + if (!sz_piece)
> + return -EINVAL;
> +
> + r->ar.end = r->ar.start + sz_piece;
> + next = damon_next_region(r);
> + for (start = r->ar.end; start + sz_piece <= orig_end;
> + start += sz_piece) {
> + n = damon_new_region(start, start + sz_piece);
> + if (!n)
> + return -ENOMEM;
> + damon_insert_region(n, r, next);
> + r = n;
> + }
> + /* complement last region for possible rounding error */
> + if (n)
> + n->ar.end = orig_end;
> +
> + return 0;
> +}

[...]

> +/*
> + * Get the three regions in the given target (task)
> + *
> + * Returns 0 on success, negative error code otherwise.
> + */
> +static int damon_va_three_regions(struct damon_target *t,
> + struct damon_addr_range regions[3])
> +{
> + struct mm_struct *mm;
> + int rc;
> +
> + mm = damon_get_mm(t);
> + if (!mm)
> + return -EINVAL;
> +
> + mmap_read_lock(mm);
> + rc = __damon_va_three_regions(mm->mmap, regions);
> + mmap_read_unlock(mm);

This is being called for each target every second by default. Seems
too aggressive. Applications don't change their address space every
second. I would recommend to default ctx->primitive_update_interval to
a higher default value.

> +
> + mmput(mm);
> + return rc;
> +}
> +

[...]

> +static void __damon_va_init_regions(struct damon_ctx *c,

Keep the convention of naming damon_ctx ctx.

> + struct damon_target *t)
> +{
> + struct damon_region *r;
> + struct damon_addr_range regions[3];
> + unsigned long sz = 0, nr_pieces;
> + int i;
> +
> + if (damon_va_three_regions(t, regions)) {
> + pr_err("Failed to get three regions of target %lu\n", t->id);
> + return;
> + }
> +
> + for (i = 0; i < 3; i++)
> + sz += regions[i].end - regions[i].start;
> + if (c->min_nr_regions)
> + sz /= c->min_nr_regions;
> + if (sz < DAMON_MIN_REGION)
> + sz = DAMON_MIN_REGION;
> +
> + /* Set the initial three regions of the target */
> + for (i = 0; i < 3; i++) {
> + r = damon_new_region(regions[i].start, regions[i].end);
> + if (!r) {
> + pr_err("%d'th init region creation failed\n", i);
> + return;
> + }
> + damon_add_region(r, t);
> +
> + nr_pieces = (regions[i].end - regions[i].start) / sz;
> + damon_va_evenly_split_region(c, r, nr_pieces);
> + }
> +}

[...]

> +/*
> + * Update damon regions for the three big regions of the given target
> + *
> + * t the given target
> + * bregions the three big regions of the target
> + */
> +static void damon_va_apply_three_regions(struct damon_ctx *ctx,

ctx not used in this function.


> + struct damon_target *t, struct damon_addr_range bregions[3])
> +{
> + struct damon_region *r, *next;
> + unsigned int i = 0;
> +
> + /* Remove regions which are not in the three big regions now */
> + damon_for_each_region_safe(r, next, t) {
> + for (i = 0; i < 3; i++) {
> + if (damon_intersect(r, &bregions[i]))
> + break;
> + }
> + if (i == 3)
> + damon_destroy_region(r);
> + }
> +
> + /* Adjust intersecting regions to fit with the three big regions */
> + for (i = 0; i < 3; i++) {
> + struct damon_region *first = NULL, *last;
> + struct damon_region *newr;
> + struct damon_addr_range *br;
> +
> + br = &bregions[i];
> + /* Get the first and last regions which intersects with br */
> + damon_for_each_region(r, t) {
> + if (damon_intersect(r, br)) {
> + if (!first)
> + first = r;
> + last = r;
> + }
> + if (r->ar.start >= br->end)
> + break;
> + }
> + if (!first) {
> + /* no damon_region intersects with this big region */
> + newr = damon_new_region(
> + ALIGN_DOWN(br->start,
> + DAMON_MIN_REGION),
> + ALIGN(br->end, DAMON_MIN_REGION));
> + if (!newr)
> + continue;
> + damon_insert_region(newr, damon_prev_region(r), r);
> + } else {
> + first->ar.start = ALIGN_DOWN(br->start,
> + DAMON_MIN_REGION);
> + last->ar.end = ALIGN(br->end, DAMON_MIN_REGION);
> + }
> + }
> +}

2021-06-22 18:14:26

by Shakeel Butt

Subject: Re: [PATCH v31 07/13] mm/damon: Implement a debugfs-based user space interface

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> DAMON is designed to be used by kernel space code such as the memory
> management subsystems, and therefore it provides only kernel space API.
> That said, letting the user space control DAMON could provide some
> benefits to them. For example, it will allow user space to analyze
> their specific workloads and make their own special optimizations.
>
> For such cases, this commit implements a simple DAMON application kernel
> module, namely 'damon-dbgfs', which merely wraps the DAMON api and
> exports those to the user space via the debugfs.
>
> 'damon-dbgfs' exports three files, ``attrs``, ``target_ids``, and
> ``monitor_on`` under its debugfs directory, ``<debugfs>/damon/``.
>
> Attributes
> ----------
>
> Users can read and write the ``sampling interval``, ``aggregation
> interval``, ``regions update interval``, and min/max number of
> monitoring target regions by reading from and writing to the ``attrs``
> file. For example, below commands set those values to 5 ms, 100 ms,
> 1,000 ms, 10, 1000 and check it again::
>
> # cd <debugfs>/damon
> # echo 5000 100000 1000000 10 1000 > attrs
> # cat attrs
> 5000 100000 1000000 10 1000
>
> Target IDs
> ----------
>
> Some types of address spaces supports multiple monitoring target. For
> example, the virtual memory address spaces monitoring can have multiple
> processes as the monitoring targets. Users can set the targets by
> writing relevant id values of the targets to, and get the ids of the
> current targets by reading from the ``target_ids`` file. In case of the
> virtual address spaces monitoring, the values should be pids of the
> monitoring target processes. For example, below commands set processes
> having pids 42 and 4242 as the monitoring targets and check it again::
>
> # cd <debugfs>/damon
> # echo 42 4242 > target_ids
> # cat target_ids
> 42 4242
>
> Note that setting the target ids doesn't start the monitoring.
>
> Turning On/Off
> --------------
>
> Setting the files as described above doesn't incur effect unless you
> explicitly start the monitoring. You can start, stop, and check the
> current status of the monitoring by writing to and reading from the
> ``monitor_on`` file. Writing ``on`` to the file starts the monitoring
> of the targets with the attributes. Writing ``off`` to the file stops
> those. DAMON also stops if every targets are invalidated (in case of
> the virtual memory monitoring, target processes are invalidated when
> terminated). Below example commands turn on, off, and check the status
> of DAMON::
>
> # cd <debugfs>/damon
> # echo on > monitor_on
> # echo off > monitor_on
> # cat monitor_on
> off
>
> Please note that you cannot write to the above-mentioned debugfs files
> while the monitoring is turned on. If you write to the files while
> DAMON is running, an error code such as ``-EBUSY`` will be returned.
>
> Signed-off-by: SeongJae Park <[email protected]>
> Reviewed-by: Leonard Foerster <[email protected]>
> Reviewed-by: Fernand Sieber <[email protected]>


The high level comment I have for this patch is the layering of pid
reference counting. The dbgfs should treat the targets as abstract
objects and vaddr should handle the reference counting of pids. More
specifically move find_get_pid from dbgfs to vaddr and to add an
interface to the primitive for set_targets.

At the moment, the pid reference is taken in dbgfs and put in vaddr.
This will be the source of bugs in future.

2021-06-22 18:25:00

by Shakeel Butt

Subject: Re: [PATCH v31 08/13] mm/damon/dbgfs: Export kdamond pid to the user space

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> For CPU usage accounting, knowing pid of the monitoring thread could be
> helpful. For example, users could use cpuaccount cgroups with the pid.
>
> This commit therefore exports the pid of currently running monitoring
> thread to the user space via 'kdamond_pid' file in the debugfs
> directory.
>
> Signed-off-by: SeongJae Park <[email protected]>
> Reviewed-by: Fernand Sieber <[email protected]>
> ---

[...]

>
> +static const struct file_operations kdamond_pid_fops = {
> + .owner = THIS_MODULE,

I don't think you need to set the owner (and for other fops) as these
files are built into modules. Otherwise it looks good.

2021-06-24 10:27:37

by SeongJae Park

Subject: Re: [PATCH v31 03/13] mm/damon: Adaptively adjust regions

From: SeongJae Park <[email protected]>

On Tue, 22 Jun 2021 07:59:35 -0700 Shakeel Butt <[email protected]> wrote:

> On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
> >
> > From: SeongJae Park <[email protected]>
> >
> > Even somehow the initial monitoring target regions are well constructed
> > to fulfill the assumption (pages in same region have similar access
> > frequencies), the data access pattern can be dynamically changed. This
> > will result in low monitoring quality. To keep the assumption as much
> > as possible, DAMON adaptively merges and splits each region based on
> > their access frequency.
> >
> > For each ``aggregation interval``, it compares the access frequencies of
> > adjacent regions and merges those if the frequency difference is small.
> > Then, after it reports and clears the aggregated access frequency of
> > each region, it splits each region into two or three regions if the
> > total number of regions will not exceed the user-specified maximum
> > number of regions after the split.
> >
> > In this way, DAMON provides its best-effort quality and minimal overhead
> > while keeping the upper-bound overhead that users set.
> >
> > Signed-off-by: SeongJae Park <[email protected]>
> > Reviewed-by: Leonard Foerster <[email protected]>
> > Reviewed-by: Fernand Sieber <[email protected]>
> [...]
> >
> > +unsigned int damon_nr_regions(struct damon_target *t)
> > +{
> > + struct damon_region *r;
> > + unsigned int nr_regions = 0;
> > +
> > + damon_for_each_region(r, t)
> > + nr_regions++;
>
> This bugs me everytime. Please just have nr_regions field in the
> damon_target instead of traversing the list to count the number of
> regions.

Ok, I will make the change in next spin.

>
> Other than that, it looks good to me.

Thanks,
SeongJae Park

2021-06-24 10:27:49

by SeongJae Park

Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

From: SeongJae Park <[email protected]>

On Tue, 22 Jun 2021 08:00:58 -0700 Shakeel Butt <[email protected]> wrote:

> On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
> >
> > From: SeongJae Park <[email protected]>
> >
> > This commit introduces a reference implementation of the address space
> > specific low level primitives for the virtual address space, so that
> > users of DAMON can easily monitor the data accesses on virtual address
> > spaces of specific processes by simply configuring the implementation to
> > be used by DAMON.
> >
> > The low level primitives for the fundamental access monitoring are
> > defined in two parts:
> >
> > 1. Identification of the monitoring target address range for the address
> > space.
> > 2. Access check of specific address range in the target space.
> >
> > The reference implementation for the virtual address space does the
> > works as below.
> >
> > PTE Accessed-bit Based Access Check
> > -----------------------------------
> >
> > The implementation uses PTE Accessed-bit for basic access checks. That
> > is, it clears the bit for the next sampling target page and checks
> > whether it is set again after one sampling period. This could disturb
> > the reclaim logic. DAMON uses ``PG_idle`` and ``PG_young`` page flags
> > to solve the conflict, as Idle page tracking does.
> >
> > VMA-based Target Address Range Construction
> > -------------------------------------------
> >
> > Only small parts in the super-huge virtual address space of the
> > processes are mapped to physical memory and accessed. Thus, tracking
> > the unmapped address regions is just wasteful. However, because DAMON
> > can deal with some level of noise using the adaptive regions adjustment
> > mechanism, tracking every mapping is not strictly required but could
> > even incur a high overhead in some cases. That said, too huge unmapped
> > areas inside the monitoring target should be removed to not take the
> > time for the adaptive mechanism.
> >
> > For the reason, this implementation converts the complex mappings to
> > three distinct regions that cover every mapped area of the address
> > space. Also, the two gaps between the three regions are the two biggest
> > unmapped areas in the given address space. The two biggest unmapped
> > areas would be the gap between the heap and the uppermost mmap()-ed
> > region, and the gap between the lowermost mmap()-ed region and the stack
> > in most of the cases. Because these gaps are exceptionally huge in
> > usual address spaces, excluding these will be sufficient to make a
> > reasonable trade-off. Below shows this in detail::
> >
> > <heap>
> > <BIG UNMAPPED REGION 1>
> > <uppermost mmap()-ed region>
> > (small mmap()-ed regions and munmap()-ed regions)
> > <lowermost mmap()-ed region>
> > <BIG UNMAPPED REGION 2>
> > <stack>
> >
> > Signed-off-by: SeongJae Park <[email protected]>
> > Reviewed-by: Leonard Foerster <[email protected]>
> > Reviewed-by: Fernand Sieber <[email protected]>
>
> Couple of nits below and one concern on the default value of
> primitive_update_interval of virtual address space primitive.
> Otherwise looks good to me.

Thank you!

>
> [...]
>
> > +
> > +/*
> > + * Size-evenly split a region into 'nr_pieces' small regions
> > + *
> > + * Returns 0 on success, or negative error code otherwise.
> > + */
> > +static int damon_va_evenly_split_region(struct damon_ctx *ctx,
>
> I don't see ctx being used in this function.

Good point, will remove that from the next spin.

>
> > + struct damon_region *r, unsigned int nr_pieces)
> > +{
> > + unsigned long sz_orig, sz_piece, orig_end;
> > + struct damon_region *n = NULL, *next;
> > + unsigned long start;
> > +
> > + if (!r || !nr_pieces)
> > + return -EINVAL;
> > +
> > + orig_end = r->ar.end;
> > + sz_orig = r->ar.end - r->ar.start;
> > + sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);
> > +
> > + if (!sz_piece)
> > + return -EINVAL;
> > +
> > + r->ar.end = r->ar.start + sz_piece;
> > + next = damon_next_region(r);
> > + for (start = r->ar.end; start + sz_piece <= orig_end;
> > + start += sz_piece) {
> > + n = damon_new_region(start, start + sz_piece);
> > + if (!n)
> > + return -ENOMEM;
> > + damon_insert_region(n, r, next);
> > + r = n;
> > + }
> > + /* complement last region for possible rounding error */
> > + if (n)
> > + n->ar.end = orig_end;
> > +
> > + return 0;
> > +}
>
> [...]
>
> > +/*
> > + * Get the three regions in the given target (task)
> > + *
> > + * Returns 0 on success, negative error code otherwise.
> > + */
> > +static int damon_va_three_regions(struct damon_target *t,
> > + struct damon_addr_range regions[3])
> > +{
> > + struct mm_struct *mm;
> > + int rc;
> > +
> > + mm = damon_get_mm(t);
> > + if (!mm)
> > + return -EINVAL;
> > +
> > + mmap_read_lock(mm);
> > + rc = __damon_va_three_regions(mm->mmap, regions);
> > + mmap_read_unlock(mm);
>
> This is being called for each target every second by default. Seems
> too aggressive. Applications don't change their address space every
> second. I would recommend to default ctx->primitive_update_interval to
> a higher default value.

Good point. If there are many targets and each target has a huge number of
VMAs, the overhead could be high. Nevertheless, I couldn't find the overhead
in my test setup. Also, it seems someone are already started exploring DAMON
patchset with the default value. and usages from others. Silently changing the
default value could distract such people. So, if you think it's ok, I'd like
to change the default value only after someone finds the overhead from their
usages and asks a change.

If you disagree or you found the overhead from your usage, please feel free to
let me know.

>
> > +
> > + mmput(mm);
> > + return rc;
> > +}
> > +
>
> [...]
>
> > +static void __damon_va_init_regions(struct damon_ctx *c,
>
> Keep the convention of naming damon_ctx ctx.

Ok, I will do so from the next spin.

>
> > + struct damon_target *t)
> > +{
> > + struct damon_region *r;
> > + struct damon_addr_range regions[3];
> > + unsigned long sz = 0, nr_pieces;
> > + int i;
> > +
> > + if (damon_va_three_regions(t, regions)) {
> > + pr_err("Failed to get three regions of target %lu\n", t->id);
> > + return;
> > + }
> > +
> > + for (i = 0; i < 3; i++)
> > + sz += regions[i].end - regions[i].start;
> > + if (c->min_nr_regions)
> > + sz /= c->min_nr_regions;
> > + if (sz < DAMON_MIN_REGION)
> > + sz = DAMON_MIN_REGION;
> > +
> > + /* Set the initial three regions of the target */
> > + for (i = 0; i < 3; i++) {
> > + r = damon_new_region(regions[i].start, regions[i].end);
> > + if (!r) {
> > + pr_err("%d'th init region creation failed\n", i);
> > + return;
> > + }
> > + damon_add_region(r, t);
> > +
> > + nr_pieces = (regions[i].end - regions[i].start) / sz;
> > + damon_va_evenly_split_region(c, r, nr_pieces);
> > + }
> > +}
>
> [...]
>
> > +/*
> > + * Update damon regions for the three big regions of the given target
> > + *
> > + * t the given target
> > + * bregions the three big regions of the target
> > + */
> > +static void damon_va_apply_three_regions(struct damon_ctx *ctx,
>
> ctx not used in this function.

Good eye, will remove that from the next version.

>
>
> > + struct damon_target *t, struct damon_addr_range bregions[3])
> > +{
> > + struct damon_region *r, *next;
> > + unsigned int i = 0;
> > +
> > + /* Remove regions which are not in the three big regions now */
> > + damon_for_each_region_safe(r, next, t) {
> > + for (i = 0; i < 3; i++) {
> > + if (damon_intersect(r, &bregions[i]))
> > + break;
> > + }
> > + if (i == 3)
> > + damon_destroy_region(r);
> > + }
> > +
> > + /* Adjust intersecting regions to fit with the three big regions */
> > + for (i = 0; i < 3; i++) {
> > + struct damon_region *first = NULL, *last;
> > + struct damon_region *newr;
> > + struct damon_addr_range *br;
> > +
> > + br = &bregions[i];
> > + /* Get the first and last regions which intersects with br */
> > + damon_for_each_region(r, t) {
> > + if (damon_intersect(r, br)) {
> > + if (!first)
> > + first = r;
> > + last = r;
> > + }
> > + if (r->ar.start >= br->end)
> > + break;
> > + }
> > + if (!first) {
> > + /* no damon_region intersects with this big region */
> > + newr = damon_new_region(
> > + ALIGN_DOWN(br->start,
> > + DAMON_MIN_REGION),
> > + ALIGN(br->end, DAMON_MIN_REGION));
> > + if (!newr)
> > + continue;
> > + damon_insert_region(newr, damon_prev_region(r), r);
> > + } else {
> > + first->ar.start = ALIGN_DOWN(br->start,
> > + DAMON_MIN_REGION);
> > + last->ar.end = ALIGN(br->end, DAMON_MIN_REGION);
> > + }
> > + }
> > +}


Thanks,
SeongJae Park

2021-06-24 10:27:55

by SeongJae Park

Subject: Re: [PATCH v31 01/13] mm: Introduce Data Access MONitor (DAMON)

From: SeongJae Park <[email protected]>

On Tue, 22 Jun 2021 07:59:11 -0700 Shakeel Butt <[email protected]> wrote:

> On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
> >
> > From: SeongJae Park <[email protected]>
> >
> > DAMON is a data access monitoring framework for the Linux kernel. The
> > core mechanisms of DAMON make it
> >
> > - accurate (the monitoring output is useful enough for DRAM level
> > performance-centric memory management; It might be inappropriate for
> > CPU cache levels, though),
> > - light-weight (the monitoring overhead is normally low enough to be
> > applied online), and
> > - scalable (the upper-bound of the overhead is in constant range
> > regardless of the size of target workloads).
> >
> > Using this framework, hence, we can easily write efficient kernel space
> > data access monitoring applications. For example, the kernel's memory
> > management mechanisms can make advanced decisions using this.
> > Experimental data access aware optimization works that incurring high
> > access monitoring overhead could again be implemented on top of this.
> >
> > Due to its simple and flexible interface, providing user space interface
> > would be also easy. Then, user space users who have some special
> > workloads can write personalized applications for better understanding
> > and optimizations of their workloads and systems.
> >
> > ===
> >
> > Nevertheless, this commit is defining and implementing only basic access
> > check part without the overhead-accuracy handling core logic. The basic
> > access check is as below.
> >
> > The output of DAMON says what memory regions are how frequently accessed
> > for a given duration. The resolution of the access frequency is
> > controlled by setting ``sampling interval`` and ``aggregation
> > interval``. In detail, DAMON checks access to each page per ``sampling
> > interval`` and aggregates the results. In other words, counts the
> > number of the accesses to each region. After each ``aggregation
> > interval`` passes, DAMON calls callback functions that previously
> > registered by users so that users can read the aggregated results and
> > then clears the results. This can be described in below simple
> > pseudo-code::
> >
> > init()
> > while monitoring_on:
> > for page in monitoring_target:
> > if accessed(page):
> > nr_accesses[page] += 1
> > if time() % aggregation_interval == 0:
> > for callback in user_registered_callbacks:
> > callback(monitoring_target, nr_accesses)
> > for page in monitoring_target:
> > nr_accesses[page] = 0
> > if time() % update_interval == 0:
>
> regions_update_interval?

It used the name before. But, I changed the name in this way to use it as a
general periodic updates of monitoring primitives. Of course we can use the
specific name only in this specific example, but also want to make this as
similar to the actual code as possible.

If you strongly want to rename this, please feel free to let me know.

>
> > update()
> > sleep(sampling interval)
> >
> > The target regions constructed at the beginning of the monitoring and
> > updated after each ``regions_update_interval``, because the target
> > regions could be dynamically changed (e.g., mmap() or memory hotplug).
> > The monitoring overhead of this mechanism will arbitrarily increase as
> > the size of the target workload grows.
> >
> > The basic monitoring primitives for actual access check and dynamic
> > target regions construction aren't in the core part of DAMON. Instead,
> > it allows users to implement their own primitives that are optimized for
> > their use case and configure DAMON to use those. In other words, users
> > cannot use current version of DAMON without some additional works.
> >
> > Following commits will implement the core mechanisms for the
> > overhead-accuracy control and default primitives implementations.
> >
> > Signed-off-by: SeongJae Park <[email protected]>
> > Reviewed-by: Leonard Foerster <[email protected]>
> > Reviewed-by: Fernand Sieber <[email protected]>
>
> Few nits below otherwise look good to me. You can add:
>
> Acked-by: Shakeel Butt <[email protected]>

Thank you!

>
> [...]
> > +/*
> > + * __damon_start() - Starts monitoring with given context.
> > + * @ctx: monitoring context
> > + *
> > + * This function should be called while damon_lock is hold.
> > + *
> > + * Return: 0 on success, negative error code otherwise.
> > + */
> > +static int __damon_start(struct damon_ctx *ctx)
> > +{
> > + int err = -EBUSY;
> > +
> > + mutex_lock(&ctx->kdamond_lock);
> > + if (!ctx->kdamond) {
> > + err = 0;
> > + ctx->kdamond_stop = false;
> > + ctx->kdamond = kthread_create(kdamond_fn, ctx, "kdamond.%d",
> > + nr_running_ctxs);
> > + if (IS_ERR(ctx->kdamond))
> > + err = PTR_ERR(ctx->kdamond);
> > + else
> > + wake_up_process(ctx->kdamond);
>
> Nit: You can use kthread_run() here.

Ok, I will use that from the next spin.

>
> > + }
> > + mutex_unlock(&ctx->kdamond_lock);
> > +
> > + return err;
> > +}
> > +
> [...]
> > +static int __damon_stop(struct damon_ctx *ctx)
> > +{
> > + mutex_lock(&ctx->kdamond_lock);
> > + if (ctx->kdamond) {
> > + ctx->kdamond_stop = true;
> > + mutex_unlock(&ctx->kdamond_lock);
> > + while (damon_kdamond_running(ctx))
> > + usleep_range(ctx->sample_interval,
> > + ctx->sample_interval * 2);
>
> Any reason to not use kthread_stop() here?

Using 'kthread_stop()' here will make the code much simpler. But, 'kdamond'
also stops itself when all monitoring targets became invalid (e.g., all
monitoring target processes terminated). However, 'kthread_stop()' is not easy
to be used for the use case (self stopping). It's of course possible, but it
would make the code longer. That's why I use 'kdamond_stop' flag here. So,
I'd like leave this as is. If you think 'kthread_stop()' should be used,
please feel free to let me know.


Thanks,
SeongJae Park

2021-06-24 10:28:40

by SeongJae Park

Subject: Re: [PATCH v31 07/13] mm/damon: Implement a debugfs-based user space interface

From: SeongJae Park <[email protected]>

On Tue, 22 Jun 2021 11:12:36 -0700 Shakeel Butt <[email protected]> wrote:

> On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
> >
> > From: SeongJae Park <[email protected]>
> >
> > DAMON is designed to be used by kernel space code such as the memory
> > management subsystems, and therefore it provides only kernel space API.
> > That said, letting the user space control DAMON could provide some
> > benefits to them. For example, it will allow user space to analyze
> > their specific workloads and make their own special optimizations.
> >
> > For such cases, this commit implements a simple DAMON application kernel
> > module, namely 'damon-dbgfs', which merely wraps the DAMON api and
> > exports those to the user space via the debugfs.
> >
> > 'damon-dbgfs' exports three files, ``attrs``, ``target_ids``, and
> > ``monitor_on`` under its debugfs directory, ``<debugfs>/damon/``.
> >
> > Attributes
> > ----------
> >
> > Users can read and write the ``sampling interval``, ``aggregation
> > interval``, ``regions update interval``, and min/max number of
> > monitoring target regions by reading from and writing to the ``attrs``
> > file. For example, below commands set those values to 5 ms, 100 ms,
> > 1,000 ms, 10, 1000 and check it again::
> >
> > # cd <debugfs>/damon
> > # echo 5000 100000 1000000 10 1000 > attrs
> > # cat attrs
> > 5000 100000 1000000 10 1000
> >
> > Target IDs
> > ----------
> >
> > Some types of address spaces supports multiple monitoring target. For
> > example, the virtual memory address spaces monitoring can have multiple
> > processes as the monitoring targets. Users can set the targets by
> > writing relevant id values of the targets to, and get the ids of the
> > current targets by reading from the ``target_ids`` file. In case of the
> > virtual address spaces monitoring, the values should be pids of the
> > monitoring target processes. For example, below commands set processes
> > having pids 42 and 4242 as the monitoring targets and check it again::
> >
> > # cd <debugfs>/damon
> > # echo 42 4242 > target_ids
> > # cat target_ids
> > 42 4242
> >
> > Note that setting the target ids doesn't start the monitoring.
> >
> > Turning On/Off
> > --------------
> >
> > Setting the files as described above doesn't incur effect unless you
> > explicitly start the monitoring. You can start, stop, and check the
> > current status of the monitoring by writing to and reading from the
> > ``monitor_on`` file. Writing ``on`` to the file starts the monitoring
> > of the targets with the attributes. Writing ``off`` to the file stops
> > those. DAMON also stops if every targets are invalidated (in case of
> > the virtual memory monitoring, target processes are invalidated when
> > terminated). Below example commands turn on, off, and check the status
> > of DAMON::
> >
> > # cd <debugfs>/damon
> > # echo on > monitor_on
> > # echo off > monitor_on
> > # cat monitor_on
> > off
> >
> > Please note that you cannot write to the above-mentioned debugfs files
> > while the monitoring is turned on. If you write to the files while
> > DAMON is running, an error code such as ``-EBUSY`` will be returned.
> >
> > Signed-off-by: SeongJae Park <[email protected]>
> > Reviewed-by: Leonard Foerster <[email protected]>
> > Reviewed-by: Fernand Sieber <[email protected]>
>
>
> The high level comment I have for this patch is the layering of pid
> reference counting. The dbgfs should treat the targets as abstract
> objects and vaddr should handle the reference counting of pids. More
> specifically move find_get_pid from dbgfs to vaddr and to add an
> interface to the primitive for set_targets.
>
> At the moment, the pid reference is taken in dbgfs and put in vaddr.
> This will be the source of bugs in future.

Good point, and agreed on the problem. But, I'd like to move 'put_pid()' to
dbgfs, because I think that would let extending the dbgfs user interface to
pidfd a little bit simpler. Also, I think that would be easier to use for
in-kernel programming interface usages. If you disagree, please feel free to
let me know.


Thanks,
SeongJae Park

2021-06-24 10:28:42

by SeongJae Park

Subject: Re: [PATCH v31 08/13] mm/damon/dbgfs: Export kdamond pid to the user space

From: SeongJae Park <[email protected]>

On Tue, 22 Jun 2021 11:23:12 -0700 Shakeel Butt <[email protected]> wrote:

> On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
> >
> > From: SeongJae Park <[email protected]>
> >
> > For CPU usage accounting, knowing pid of the monitoring thread could be
> > helpful. For example, users could use cpuaccount cgroups with the pid.
> >
> > This commit therefore exports the pid of currently running monitoring
> > thread to the user space via 'kdamond_pid' file in the debugfs
> > directory.
> >
> > Signed-off-by: SeongJae Park <[email protected]>
> > Reviewed-by: Fernand Sieber <[email protected]>
> > ---
>
> [...]
>
> >
> > +static const struct file_operations kdamond_pid_fops = {
> > + .owner = THIS_MODULE,
>
> I don't think you need to set the owner (and for other fops) as these
> files are built into modules. Otherwise it looks good.

Good point. Will remove those from the next spin.


Thanks,
SeongJae Park

2021-06-24 14:36:16

by Shakeel Butt

Subject: Re: [PATCH v31 01/13] mm: Introduce Data Access MONitor (DAMON)

On Thu, Jun 24, 2021 at 3:26 AM SeongJae Park <[email protected]> wrote:
>
[...]
> > > if time() % update_interval == 0:
> >
> > regions_update_interval?
>
> It used the name before. But, I changed the name in this way to use it as a
> general periodic updates of monitoring primitives. Of course we can use the
> specific name only in this specific example, but also want to make this as
> similar to the actual code as possible.
>
> If you strongly want to rename this, please feel free to let me know.
>

Nah, it is ok.

[...]

> >
> > Any reason to not use kthread_stop() here?
>
> Using 'kthread_stop()' here will make the code much simpler. But, 'kdamond'
> also stops itself when all monitoring targets became invalid (e.g., all
> monitoring target processes terminated). However, 'kthread_stop()' is not easy
> to be used for the use case (self stopping). It's of course possible, but it
> would make the code longer. That's why I use 'kdamond_stop' flag here. So,
> I'd like leave this as is. If you think 'kthread_stop()' should be used,
> please feel free to let me know.
>

Fine as it is.

2021-06-24 14:44:19

by Shakeel Butt

Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

On Thu, Jun 24, 2021 at 3:26 AM SeongJae Park <[email protected]> wrote:
>
[...]
> > > +/*
> > > + * Get the three regions in the given target (task)
> > > + *
> > > + * Returns 0 on success, negative error code otherwise.
> > > + */
> > > +static int damon_va_three_regions(struct damon_target *t,
> > > + struct damon_addr_range regions[3])
> > > +{
> > > + struct mm_struct *mm;
> > > + int rc;
> > > +
> > > + mm = damon_get_mm(t);
> > > + if (!mm)
> > > + return -EINVAL;
> > > +
> > > + mmap_read_lock(mm);
> > > + rc = __damon_va_three_regions(mm->mmap, regions);
> > > + mmap_read_unlock(mm);
> >
> > This is being called for each target every second by default. Seems
> > too aggressive. Applications don't change their address space every
> > second. I would recommend to default ctx->primitive_update_interval to
> > a higher default value.
>
> Good point. If there are many targets and each target has a huge number of
> VMAs, the overhead could be high. Nevertheless, I couldn't find the overhead
> in my test setup. Also, it seems someone are already started exploring DAMON
> patchset with the default value. and usages from others. Silently changing the
> default value could distract such people. So, if you think it's ok, I'd like
> to change the default value only after someone finds the overhead from their
> usages and asks a change.
>
> If you disagree or you found the overhead from your usage, please feel free to
> let me know.
>

mmap lock is a source contention in the real world workloads. We do
observe in our fleet and many others (like Facebook) do complain on
this issue. This is the whole motivation behind SFP, maple tree and
many other mmap lock scalability work. I would be really careful to
add another source of contention on mmap lock. Yes, the user can
change this interval themselves but we should not burden them with
this internal knowledge like "oh if you observe high mmap contention
you may want to increase this specific interval". We should set a good
default value to avoid such situations (most of the time).

2021-06-24 14:55:13

by Shakeel Butt

Subject: Re: [PATCH v31 07/13] mm/damon: Implement a debugfs-based user space interface

On Thu, Jun 24, 2021 at 3:26 AM SeongJae Park <[email protected]> wrote:
>
[...]
> >
> > The high level comment I have for this patch is the layering of pid
> > reference counting. The dbgfs should treat the targets as abstract
> > objects and vaddr should handle the reference counting of pids. More
> > specifically move find_get_pid from dbgfs to vaddr and to add an
> > interface to the primitive for set_targets.
> >
> > At the moment, the pid reference is taken in dbgfs and put in vaddr.
> > This will be the source of bugs in future.
>
> Good point, and agreed on the problem. But, I'd like to move 'put_pid()' to
> dbgfs, because I think that would let extending the dbgfs user interface to
> pidfd a little bit simpler. Also, I think that would be easier to use for
> in-kernel programming interface usages. If you disagree, please feel free to
> let me know.
>

I was thinking of removing targetid_is_pid() checks. Anyways this is
not something we can not change later, so I will let you decide which
direction you want to take.

2021-06-24 15:22:58

by SeongJae Park

Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

From: SeongJae Park <[email protected]>

On Thu, 24 Jun 2021 07:42:44 -0700 Shakeel Butt <[email protected]> wrote:

> On Thu, Jun 24, 2021 at 3:26 AM SeongJae Park <[email protected]> wrote:
> >
> [...]
> > > > +/*
> > > > + * Get the three regions in the given target (task)
> > > > + *
> > > > + * Returns 0 on success, negative error code otherwise.
> > > > + */
> > > > +static int damon_va_three_regions(struct damon_target *t,
> > > > + struct damon_addr_range regions[3])
> > > > +{
> > > > + struct mm_struct *mm;
> > > > + int rc;
> > > > +
> > > > + mm = damon_get_mm(t);
> > > > + if (!mm)
> > > > + return -EINVAL;
> > > > +
> > > > + mmap_read_lock(mm);
> > > > + rc = __damon_va_three_regions(mm->mmap, regions);
> > > > + mmap_read_unlock(mm);
> > >
> > > This is being called for each target every second by default. Seems
> > > too aggressive. Applications don't change their address space every
> > > second. I would recommend to default ctx->primitive_update_interval to
> > > a higher default value.
> >
> > Good point. If there are many targets and each target has a huge number of
> > VMAs, the overhead could be high. Nevertheless, I couldn't find the overhead
> > in my test setup. Also, it seems someone are already started exploring DAMON
> > patchset with the default value. and usages from others. Silently changing the
> > default value could distract such people. So, if you think it's ok, I'd like
> > to change the default value only after someone finds the overhead from their
> > usages and asks a change.
> >
> > If you disagree or you found the overhead from your usage, please feel free to
> > let me know.
> >
>
> mmap lock is a source contention in the real world workloads. We do
> observe in our fleet and many others (like Facebook) do complain on
> this issue. This is the whole motivation behind SFP, maple tree and
> many other mmap lock scalability work. I would be really careful to
> add another source of contention on mmap lock. Yes, the user can
> change this interval themselves but we should not burden them with
> this internal knowledge like "oh if you observe high mmap contention
> you may want to increase this specific interval". We should set a good
> default value to avoid such situations (most of the time).

Thank you for this nice clarification. I can understand your concern because I
also worked for an HTM-based solution of the scalability issue before.

However, I have neither strong preference nor confidence for the new default
value at the moment. Could you please recommend one if you have?


Thanks,
SeongJae Park

2021-06-24 16:35:24

by Shakeel Butt

Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

On Thu, Jun 24, 2021 at 8:21 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> On Thu, 24 Jun 2021 07:42:44 -0700 Shakeel Butt <[email protected]> wrote:
>
> > On Thu, Jun 24, 2021 at 3:26 AM SeongJae Park <[email protected]> wrote:
> > >
> > [...]
> > > > > +/*
> > > > > + * Get the three regions in the given target (task)
> > > > > + *
> > > > > + * Returns 0 on success, negative error code otherwise.
> > > > > + */
> > > > > +static int damon_va_three_regions(struct damon_target *t,
> > > > > + struct damon_addr_range regions[3])
> > > > > +{
> > > > > + struct mm_struct *mm;
> > > > > + int rc;
> > > > > +
> > > > > + mm = damon_get_mm(t);
> > > > > + if (!mm)
> > > > > + return -EINVAL;
> > > > > +
> > > > > + mmap_read_lock(mm);
> > > > > + rc = __damon_va_three_regions(mm->mmap, regions);
> > > > > + mmap_read_unlock(mm);
> > > >
> > > > This is being called for each target every second by default. Seems
> > > > too aggressive. Applications don't change their address space every
> > > > second. I would recommend to default ctx->primitive_update_interval to
> > > > a higher default value.
> > >
> > > Good point. If there are many targets and each target has a huge number of
> > > VMAs, the overhead could be high. Nevertheless, I couldn't find the overhead
> > > in my test setup. Also, it seems someone are already started exploring DAMON
> > > patchset with the default value. and usages from others. Silently changing the
> > > default value could distract such people. So, if you think it's ok, I'd like
> > > to change the default value only after someone finds the overhead from their
> > > usages and asks a change.
> > >
> > > If you disagree or you found the overhead from your usage, please feel free to
> > > let me know.
> > >
> >
> > mmap lock is a source contention in the real world workloads. We do
> > observe in our fleet and many others (like Facebook) do complain on
> > this issue. This is the whole motivation behind SFP, maple tree and
> > many other mmap lock scalability work. I would be really careful to
> > add another source of contention on mmap lock. Yes, the user can
> > change this interval themselves but we should not burden them with
> > this internal knowledge like "oh if you observe high mmap contention
> > you may want to increase this specific interval". We should set a good
> > default value to avoid such situations (most of the time).
>
> Thank you for this nice clarification. I can understand your concern because I
> also worked for an HTM-based solution of the scalability issue before.
>
> However, I have neither strong preference nor confidence for the new default
> value at the moment. Could you please recommend one if you have?
>

I would say go with a conservative value like 60 seconds. Though there
is no scientific reason behind this specific number, I think it would
be a good compromise. Applications usually don't change their address
space layout that often.

2021-06-24 17:40:50

by SeongJae Park

Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

From: SeongJae Park <[email protected]>

On Thu, 24 Jun 2021 09:33:07 -0700 Shakeel Butt <[email protected]> wrote:

> On Thu, Jun 24, 2021 at 8:21 AM SeongJae Park <[email protected]> wrote:
> >
> > From: SeongJae Park <[email protected]>
> >
> > On Thu, 24 Jun 2021 07:42:44 -0700 Shakeel Butt <[email protected]> wrote:
> >
> > > On Thu, Jun 24, 2021 at 3:26 AM SeongJae Park <[email protected]> wrote:
> > > >
> > > [...]
> > > > > > +/*
> > > > > > + * Get the three regions in the given target (task)
> > > > > > + *
> > > > > > + * Returns 0 on success, negative error code otherwise.
> > > > > > + */
> > > > > > +static int damon_va_three_regions(struct damon_target *t,
> > > > > > + struct damon_addr_range regions[3])
> > > > > > +{
> > > > > > + struct mm_struct *mm;
> > > > > > + int rc;
> > > > > > +
> > > > > > + mm = damon_get_mm(t);
> > > > > > + if (!mm)
> > > > > > + return -EINVAL;
> > > > > > +
> > > > > > + mmap_read_lock(mm);
> > > > > > + rc = __damon_va_three_regions(mm->mmap, regions);
> > > > > > + mmap_read_unlock(mm);
> > > > >
> > > > > This is being called for each target every second by default. Seems
> > > > > too aggressive. Applications don't change their address space every
> > > > > second. I would recommend to default ctx->primitive_update_interval to
> > > > > a higher default value.
> > > >
> > > > Good point. If there are many targets and each target has a huge number of
> > > > VMAs, the overhead could be high. Nevertheless, I couldn't find the overhead
> > > > in my test setup. Also, it seems someone are already started exploring DAMON
> > > > patchset with the default value. and usages from others. Silently changing the
> > > > default value could distract such people. So, if you think it's ok, I'd like
> > > > to change the default value only after someone finds the overhead from their
> > > > usages and asks a change.
> > > >
> > > > If you disagree or you found the overhead from your usage, please feel free to
> > > > let me know.
> > > >
> > >
> > > mmap lock is a source contention in the real world workloads. We do
> > > observe in our fleet and many others (like Facebook) do complain on
> > > this issue. This is the whole motivation behind SFP, maple tree and
> > > many other mmap lock scalability work. I would be really careful to
> > > add another source of contention on mmap lock. Yes, the user can
> > > change this interval themselves but we should not burden them with
> > > this internal knowledge like "oh if you observe high mmap contention
> > > you may want to increase this specific interval". We should set a good
> > > default value to avoid such situations (most of the time).
> >
> > Thank you for this nice clarification. I can understand your concern because I
> > also worked for an HTM-based solution of the scalability issue before.
> >
> > However, I have neither strong preference nor confidence for the new default
> > value at the moment. Could you please recommend one if you have?
> >
>
> I would say go with a conservative value like 60 seconds. Though there
> is no scientific reason behind this specific number, I think it would
> be a good compromise. Applications usually don't change their address
> space layout that often.

Ok, I will use that from the next spin. Thank you for this nice suggestion.


Thanks,
SeongJae Park

2021-07-01 00:19:04

by Shakeel Butt

Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
>
> From: SeongJae Park <[email protected]>
>
> This commit introduces a reference implementation of the address space
> specific low level primitives for the virtual address space, so that
> users of DAMON can easily monitor the data accesses on virtual address
> spaces of specific processes by simply configuring the implementation to
> be used by DAMON.
>
> The low level primitives for the fundamental access monitoring are
> defined in two parts:
>
> 1. Identification of the monitoring target address range for the address
> space.
> 2. Access check of specific address range in the target space.
>
> The reference implementation for the virtual address space does the
> works as below.
>
> PTE Accessed-bit Based Access Check
> -----------------------------------
>
> The implementation uses PTE Accessed-bit for basic access checks. That
> is, it clears the bit for the next sampling target page and checks
> whether it is set again after one sampling period. This could disturb
> the reclaim logic. DAMON uses ``PG_idle`` and ``PG_young`` page flags
> to solve the conflict, as Idle page tracking does.
>
> VMA-based Target Address Range Construction
> -------------------------------------------
>
> Only small parts in the super-huge virtual address space of the
> processes are mapped to physical memory and accessed. Thus, tracking
> the unmapped address regions is just wasteful. However, because DAMON
> can deal with some level of noise using the adaptive regions adjustment
> mechanism, tracking every mapping is not strictly required but could
> even incur a high overhead in some cases. That said, too huge unmapped
> areas inside the monitoring target should be removed to not take the
> time for the adaptive mechanism.
>
> For the reason, this implementation converts the complex mappings to
> three distinct regions that cover every mapped area of the address
> space. Also, the two gaps between the three regions are the two biggest
> unmapped areas in the given address space. The two biggest unmapped
> areas would be the gap between the heap and the uppermost mmap()-ed
> region, and the gap between the lowermost mmap()-ed region and the stack
> in most of the cases. Because these gaps are exceptionally huge in
> usual address spaces, excluding these will be sufficient to make a
> reasonable trade-off. Below shows this in detail::
>
> <heap>
> <BIG UNMAPPED REGION 1>
> <uppermost mmap()-ed region>
> (small mmap()-ed regions and munmap()-ed regions)
> <lowermost mmap()-ed region>
> <BIG UNMAPPED REGION 2>
> <stack>
>
> Signed-off-by: SeongJae Park <[email protected]>
> Reviewed-by: Leonard Foerster <[email protected]>
> Reviewed-by: Fernand Sieber <[email protected]>

Acked-by: Shakeel Butt <[email protected]>

2021-07-01 00:20:08

by Shakeel Butt

Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces

On Wed, Jun 30, 2021 at 5:18 PM Shakeel Butt <[email protected]> wrote:
>
> On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <[email protected]> wrote:
> >
> > From: SeongJae Park <[email protected]>
> >
> > This commit introduces a reference implementation of the address space
> > specific low level primitives for the virtual address space, so that
> > users of DAMON can easily monitor the data accesses on virtual address
> > spaces of specific processes by simply configuring the implementation to
> > be used by DAMON.
> >
> > The low level primitives for the fundamental access monitoring are
> > defined in two parts:
> >
> > 1. Identification of the monitoring target address range for the address
> > space.
> > 2. Access check of specific address range in the target space.
> >
> > The reference implementation for the virtual address space does the
> > works as below.
> >
> > PTE Accessed-bit Based Access Check
> > -----------------------------------
> >
> > The implementation uses PTE Accessed-bit for basic access checks. That
> > is, it clears the bit for the next sampling target page and checks
> > whether it is set again after one sampling period. This could disturb
> > the reclaim logic. DAMON uses ``PG_idle`` and ``PG_young`` page flags
> > to solve the conflict, as Idle page tracking does.
> >
> > VMA-based Target Address Range Construction
> > -------------------------------------------
> >
> > Only small parts in the super-huge virtual address space of the
> > processes are mapped to physical memory and accessed. Thus, tracking
> > the unmapped address regions is just wasteful. However, because DAMON
> > can deal with some level of noise using the adaptive regions adjustment
> > mechanism, tracking every mapping is not strictly required but could
> > even incur a high overhead in some cases. That said, too huge unmapped
> > areas inside the monitoring target should be removed to not take the
> > time for the adaptive mechanism.
> >
> > For the reason, this implementation converts the complex mappings to
> > three distinct regions that cover every mapped area of the address
> > space. Also, the two gaps between the three regions are the two biggest
> > unmapped areas in the given address space. The two biggest unmapped
> > areas would be the gap between the heap and the uppermost mmap()-ed
> > region, and the gap between the lowermost mmap()-ed region and the stack
> > in most of the cases. Because these gaps are exceptionally huge in
> > usual address spaces, excluding these will be sufficient to make a
> > reasonable trade-off. Below shows this in detail::
> >
> > <heap>
> > <BIG UNMAPPED REGION 1>
> > <uppermost mmap()-ed region>
> > (small mmap()-ed regions and munmap()-ed regions)
> > <lowermost mmap()-ed region>
> > <BIG UNMAPPED REGION 2>
> > <stack>
> >
> > Signed-off-by: SeongJae Park <[email protected]>
> > Reviewed-by: Leonard Foerster <[email protected]>
> > Reviewed-by: Fernand Sieber <[email protected]>
>
> Acked-by: Shakeel Butt <[email protected]>

Ok that was by mistake. The ACK is for v32.