Changelog:
v3:
* Fix some minor formatting issues and build errors.
* Add the new syscall entry to missing architecture syscall tables.
(patch 3).
* Add flags argument for the syscall. (patch 3).
* Clean up the recency refactoring (patch 2) (suggested by Yu Zhao)
* Add the new Kconfig (CONFIG_CACHESTAT) to disable the syscall.
(patch 3) (suggested by Josh Triplett)
v2:
* len == 0 means query to EOF. len < 0 is invalid.
(patch 3) (suggested by Brian Foster)
* Make cachestat extensible by adding the `cstat_size` argument in the
syscall (patch 3)
There is currently no good way to query the page cache state of large
file sets and directory trees. There is mincore(), but it scales poorly:
the kernel writes out a lot of bitmap data that userspace has to
aggregate, when the user really doesn not care about per-page information
in that case. The user also needs to mmap and unmap each file as it goes
along, which can be quite slow as well.
This series of patches introduces a new system call, cachestat, that
summarizes the page cache statistics (number of cached pages, dirty
pages, pages marked for writeback, evicted pages etc.) of a file, in a
specified range of bytes. It also include a selftest suite that tests some
typical usage
This interface is inspired by past discussion and concerns with fincore,
which has a similar design (and as a result, issues) as mincore.
Relevant links:
https://lkml.indiana.edu/hypermail/linux/kernel/1302.1/04207.html
https://lkml.indiana.edu/hypermail/linux/kernel/1302.1/04209.html
For comparison with mincore, I ran both syscalls on a 2TB sparse file:
Using mincore:
real 0m37.510s
user 0m2.934s
sys 0m34.558s
Using cachestat:
real 0m0.009s
user 0m0.000s
sys 0m0.009s
This series consist of 4 patches:
Johannes Weiner (1):
workingset: fix confusion around eviction vs refault container
Nhat Pham (3):
workingset: refactor LRU refault to expose refault recency check
cachestat: implement cachestat syscall
selftests: Add selftests for cachestat
MAINTAINERS | 8 +
arch/alpha/kernel/syscalls/syscall.tbl | 1 +
arch/arm/tools/syscall.tbl | 1 +
arch/ia64/kernel/syscalls/syscall.tbl | 1 +
arch/m68k/kernel/syscalls/syscall.tbl | 1 +
arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
arch/parisc/kernel/syscalls/syscall.tbl | 1 +
arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
arch/s390/kernel/syscalls/syscall.tbl | 1 +
arch/sh/kernel/syscalls/syscall.tbl | 1 +
arch/sparc/kernel/syscalls/syscall.tbl | 1 +
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
include/linux/swap.h | 1 +
include/linux/syscalls.h | 3 +
include/uapi/asm-generic/unistd.h | 5 +-
include/uapi/linux/mman.h | 9 +
init/Kconfig | 10 +
kernel/sys_ni.c | 1 +
mm/Makefile | 1 +
mm/cachestat.c | 117 +++++++++++
mm/workingset.c | 130 ++++++++----
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/cachestat/.gitignore | 2 +
tools/testing/selftests/cachestat/Makefile | 7 +
.../selftests/cachestat/test_cachestat.c | 186 ++++++++++++++++++
27 files changed, 455 insertions(+), 39 deletions(-)
create mode 100644 mm/cachestat.c
create mode 100644 tools/testing/selftests/cachestat/.gitignore
create mode 100644 tools/testing/selftests/cachestat/Makefile
create mode 100644 tools/testing/selftests/cachestat/test_cachestat.c
--
2.30.2
From: Johannes Weiner <[email protected]>
Refault decisions are made based on the lruvec where the page was
evicted, as that determined its LRU order while it was alive. Stats
and workingset aging must then occur on the lruvec of the new page, as
that's the node and cgroup that experience the refault and that's the
lruvec whose nonresident info ages out by a new resident page. Those
lruvecs could be different when a page is shared between cgroups, or
the refaulting page is allocated on a different node.
There are currently two mix-ups:
1. When swap is available, the resident anon set must be considered
when comparing the refault distance. The comparison is made against
the right anon set, but the check for swap is not. When pages get
evicted from a cgroup with swap, and refault in one without, this
can incorrectly consider a hot refault as cold - and vice
versa. Fix that by using the eviction cgroup for the swap check.
2. The stats and workingset age are updated against the wrong lruvec
altogether: the right cgroup but the wrong NUMA node. When a page
refaults on a different NUMA node, this will have confusing stats
and distort the workingset age on a different lruvec - again
possibly resulting in hot/cold misclassifications down the line.
Fix the swap check and the refault pgdat to address both concerns.
This was found during code review. It hasn't caused notable issues in
production, suggesting that those refault-migrations are relatively
rare in practice.
Signed-off-by: Johannes Weiner <[email protected]>
Co-developed-by: Nhat Pham <[email protected]>
Signed-off-by: Nhat Pham <[email protected]>
---
mm/workingset.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/workingset.c b/mm/workingset.c
index ae7e984b23c6..79585d55c45d 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -457,6 +457,7 @@ void workingset_refault(struct folio *folio, void *shadow)
*/
nr = folio_nr_pages(folio);
memcg = folio_memcg(folio);
+ pgdat = folio_pgdat(folio);
lruvec = mem_cgroup_lruvec(memcg, pgdat);
mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
@@ -474,7 +475,7 @@ void workingset_refault(struct folio *folio, void *shadow)
workingset_size += lruvec_page_state(eviction_lruvec,
NR_INACTIVE_FILE);
}
- if (mem_cgroup_get_nr_swap_pages(memcg) > 0) {
+ if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) {
workingset_size += lruvec_page_state(eviction_lruvec,
NR_ACTIVE_ANON);
if (file) {
--
2.30.2
In preparation for computing recently evicted pages in cachestat,
refactor workingset_refault and lru_gen_refault to expose a helper
function that would test if an evicted page is recently evicted.
Signed-off-by: Nhat Pham <[email protected]>
---
include/linux/swap.h | 1 +
mm/workingset.c | 129 ++++++++++++++++++++++++++++++-------------
2 files changed, 92 insertions(+), 38 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index a18cf4b7c724..dae6f6f955eb 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -361,6 +361,7 @@ static inline void folio_set_swap_entry(struct folio *folio, swp_entry_t entry)
}
/* linux/mm/workingset.c */
+bool workingset_test_recent(void *shadow, bool file, bool *workingset);
void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages);
void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg);
void workingset_refault(struct folio *folio, void *shadow);
diff --git a/mm/workingset.c b/mm/workingset.c
index 79585d55c45d..4a06869392a1 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -244,6 +244,33 @@ static void *lru_gen_eviction(struct folio *folio)
return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
}
+/*
+ * Test if the folio is recently evicted.
+ *
+ * As a side effect, also populates the references with
+ * values unpacked from the shadow of the evicted folio.
+ */
+static bool lru_gen_test_recent(void *shadow, bool file, bool *workingset)
+{
+ struct mem_cgroup *eviction_memcg;
+ struct lruvec *lruvec;
+ struct lru_gen_struct *lrugen;
+ unsigned long min_seq;
+
+ int memcgid;
+ struct pglist_data *pgdat;
+ unsigned long token;
+
+ unpack_shadow(shadow, &memcgid, &pgdat, &token, workingset);
+ eviction_memcg = mem_cgroup_from_id(*memcgid);
+
+ lruvec = mem_cgroup_lruvec(eviction_memcg, *pgdat);
+ lrugen = &lruvec->lrugen;
+
+ min_seq = READ_ONCE(lrugen->min_seq[file]);
+ return !((*token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)));
+}
+
static void lru_gen_refault(struct folio *folio, void *shadow)
{
int hist, tier, refs;
@@ -306,6 +333,11 @@ static void *lru_gen_eviction(struct folio *folio)
return NULL;
}
+static bool lru_gen_test_recent(void *shadow, bool file, bool *workingset)
+{
+ return true;
+}
+
static void lru_gen_refault(struct folio *folio, void *shadow)
{
}
@@ -373,40 +405,31 @@ void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
folio_test_workingset(folio));
}
-/**
- * workingset_refault - Evaluate the refault of a previously evicted folio.
- * @folio: The freshly allocated replacement folio.
- * @shadow: Shadow entry of the evicted folio.
+/*
+ * Test if the folio is recently evicted by checking if
+ * refault distance of shadow exceeds workingset size.
*
- * Calculates and evaluates the refault distance of the previously
- * evicted folio in the context of the node and the memcg whose memory
- * pressure caused the eviction.
+ * As a side effect, populate workingset with the value
+ * unpacked from shadow.
*/
-void workingset_refault(struct folio *folio, void *shadow)
+bool workingset_test_recent(void *shadow, bool file, bool *workingset)
{
- bool file = folio_is_file_lru(folio);
struct mem_cgroup *eviction_memcg;
struct lruvec *eviction_lruvec;
unsigned long refault_distance;
unsigned long workingset_size;
- struct pglist_data *pgdat;
- struct mem_cgroup *memcg;
- unsigned long eviction;
- struct lruvec *lruvec;
unsigned long refault;
- bool workingset;
+
int memcgid;
- long nr;
+ struct pglist_data *pgdat;
+ unsigned long eviction;
- if (lru_gen_enabled()) {
- lru_gen_refault(folio, shadow);
- return;
- }
+ if (lru_gen_enabled())
+ return lru_gen_test_recent(shadow, file, workingset);
- unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
+ unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset);
eviction <<= bucket_order;
- rcu_read_lock();
/*
* Look up the memcg associated with the stored ID. It might
* have been deleted since the folio's eviction.
@@ -425,7 +448,8 @@ void workingset_refault(struct folio *folio, void *shadow)
*/
eviction_memcg = mem_cgroup_from_id(memcgid);
if (!mem_cgroup_disabled() && !eviction_memcg)
- goto out;
+ return false;
+
eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
refault = atomic_long_read(&eviction_lruvec->nonresident_age);
@@ -447,21 +471,6 @@ void workingset_refault(struct folio *folio, void *shadow)
*/
refault_distance = (refault - eviction) & EVICTION_MASK;
- /*
- * The activation decision for this folio is made at the level
- * where the eviction occurred, as that is where the LRU order
- * during folio reclaim is being determined.
- *
- * However, the cgroup that will own the folio is the one that
- * is actually experiencing the refault event.
- */
- nr = folio_nr_pages(folio);
- memcg = folio_memcg(folio);
- pgdat = folio_pgdat(folio);
- lruvec = mem_cgroup_lruvec(memcg, pgdat);
-
- mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
-
mem_cgroup_flush_stats_delayed();
/*
* Compare the distance to the existing workingset size. We
@@ -483,8 +492,51 @@ void workingset_refault(struct folio *folio, void *shadow)
NR_INACTIVE_ANON);
}
}
- if (refault_distance > workingset_size)
+
+ return refault_distance <= workingset_size;
+}
+
+/**
+ * workingset_refault - Evaluate the refault of a previously evicted folio.
+ * @folio: The freshly allocated replacement folio.
+ * @shadow: Shadow entry of the evicted folio.
+ *
+ * Calculates and evaluates the refault distance of the previously
+ * evicted folio in the context of the node and the memcg whose memory
+ * pressure caused the eviction.
+ */
+void workingset_refault(struct folio *folio, void *shadow)
+{
+ bool file = folio_is_file_lru(folio);
+ struct pglist_data *pgdat;
+ struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
+ bool workingset;
+ long nr;
+
+ if (lru_gen_enabled()) {
+ lru_gen_refault(folio, shadow);
+ return;
+ }
+
+ rcu_read_lock();
+
+ nr = folio_nr_pages(folio);
+ memcg = folio_memcg(folio);
+ pgdat = folio_pgdat(folio);
+ lruvec = mem_cgroup_lruvec(memcg, pgdat);
+
+ if (!workingset_test_recent(shadow, file, &workingset)) {
+ /*
+ * The activation decision for this folio is made at the level
+ * where the eviction occurred, as that is where the LRU order
+ * during folio reclaim is being determined.
+ *
+ * However, the cgroup that will own the folio is the one that
+ * is actually experiencing the refault event.
+ */
goto out;
+ }
folio_set_active(folio);
workingset_age_nonresident(lruvec, nr);
@@ -498,6 +550,7 @@ void workingset_refault(struct folio *folio, void *shadow)
mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
}
out:
+ mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
rcu_read_unlock();
}
--
2.30.2
Implement a new syscall that queries cache state of a file and
summarizes the number of cached pages, number of dirty pages, number of
pages marked for writeback, number of (recently) evicted pages, etc. in
a given range.
NAME
cachestat - query the page cache status of a file.
SYNOPSIS
#include <sys/mman.h>
struct cachestat {
__u64 nr_cache;
__u64 nr_dirty;
__u64 nr_writeback;
__u64 nr_evicted;
__u64 nr_recently_evicted;
};
int cachestat(unsigned int fd, off_t off, size_t len,
size_t cstat_size, struct cachestat *cstat,
unsigned int flags);
DESCRIPTION
cachestat() queries the number of cached pages, number of dirty
pages, number of pages marked for writeback, number of (recently)
evicted pages, in the bytes range given by `off` and `len`.
These values are returned in a cachestat struct, whose address is
given by the `cstat` argument.
The `off` and `len` arguments must be non-negative integers. If
`len` > 0, the queried range is [`off`, `off` + `len`]. If `len` ==
0, we will query in the range from `off` to the end of the file.
`cstat_size` allows users to obtain partial results. The syscall
will copy the first `csstat_size` bytes to the specified userspace
memory. `cstat_size` must be a non-negative value that is no larger
than the current size of the cachestat struct.
The `flags` argument is unused for now, but is included for future
extensibility. User should pass 0 (i.e no flag specified).
RETURN VALUE
On success, cachestat returns 0. On error, -1 is returned, and errno
is set to indicate the error.
ERRORS
EFAULT cstat points to an invalid address.
EINVAL invalid `cstat_size` or `flags`
EBADF invalid file descriptor.
Signed-off-by: Nhat Pham <[email protected]>
---
MAINTAINERS | 7 ++
arch/alpha/kernel/syscalls/syscall.tbl | 1 +
arch/arm/tools/syscall.tbl | 1 +
arch/ia64/kernel/syscalls/syscall.tbl | 1 +
arch/m68k/kernel/syscalls/syscall.tbl | 1 +
arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
arch/parisc/kernel/syscalls/syscall.tbl | 1 +
arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
arch/s390/kernel/syscalls/syscall.tbl | 1 +
arch/sh/kernel/syscalls/syscall.tbl | 1 +
arch/sparc/kernel/syscalls/syscall.tbl | 1 +
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
include/linux/syscalls.h | 3 +
include/uapi/asm-generic/unistd.h | 5 +-
include/uapi/linux/mman.h | 9 ++
init/Kconfig | 10 ++
kernel/sys_ni.c | 1 +
mm/Makefile | 1 +
mm/cachestat.c | 117 ++++++++++++++++++++
21 files changed, 165 insertions(+), 1 deletion(-)
create mode 100644 mm/cachestat.c
diff --git a/MAINTAINERS b/MAINTAINERS
index a198da986146..baa081a1fe52 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4552,6 +4552,13 @@ S: Supported
F: Documentation/filesystems/caching/cachefiles.rst
F: fs/cachefiles/
+CACHESTAT: PAGE CACHE STATS FOR A FILE
+M: Nhat Pham <[email protected]>
+M: Johannes Weiner <[email protected]>
+L: [email protected]
+S: Maintained
+F: mm/cachestat.c
+
CADENCE MIPI-CSI2 BRIDGES
M: Maxime Ripard <[email protected]>
L: [email protected]
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 8ebacf37a8cf..1f13995d00d7 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -490,3 +490,4 @@
558 common process_mrelease sys_process_mrelease
559 common futex_waitv sys_futex_waitv
560 common set_mempolicy_home_node sys_ni_syscall
+561 common cachestat sys_cachestat
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index ac964612d8b0..8ebed8a13874 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -464,3 +464,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index 72c929d9902b..f8c74ffeeefb 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -371,3 +371,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index b1f3940bc298..4f504783371f 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -450,3 +450,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 820145e47350..858d22bf275c 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -456,3 +456,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index 8a99c998da9b..7c84a72306d1 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -448,3 +448,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 2bca64f96164..937460f0a8ec 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -530,3 +530,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 nospu set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 799147658dee..7df0329d46cb 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -453,3 +453,4 @@
448 common process_mrelease sys_process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat sys_cachestat
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 2de85c977f54..97377e8c5025 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -453,3 +453,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 4398cc6fb68d..faa835f3c54a 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -496,3 +496,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 320480a8db4f..bc0a3c941b35 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -455,3 +455,4 @@
448 i386 process_mrelease sys_process_mrelease
449 i386 futex_waitv sys_futex_waitv
450 i386 set_mempolicy_home_node sys_set_mempolicy_home_node
+451 i386 cachestat sys_cachestat
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index c84d12608cd2..8eed4cdc7965 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -372,6 +372,7 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
#
# Due to a historical design error, certain syscalls are numbered differently
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 52c94ab5c205..2b69c3c035b6 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -421,3 +421,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a34b0f9a9972..50f8c6999d99 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -72,6 +72,7 @@ struct open_how;
struct mount_attr;
struct landlock_ruleset_attr;
enum landlock_rule_type;
+struct cachestat;
#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -1056,6 +1057,8 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
unsigned long home_node,
unsigned long flags);
+asmlinkage long sys_cachestat(unsigned int fd, off_t off, size_t len,
+ size_t cstat_size, struct cachestat __user *cstat, unsigned int flags);
/*
* Architecture-specific system calls
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 45fa180cc56a..cd639fae9086 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
#define __NR_set_mempolicy_home_node 450
__SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
+#define __NR_cachestat 451
+__SYSCALL(__NR_cachestat, sys_cachestat)
+
#undef __NR_syscalls
-#define __NR_syscalls 451
+#define __NR_syscalls 452
/*
* 32 bit systems traditionally used different
diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
index f55bc680b5b0..fe03ed0b7587 100644
--- a/include/uapi/linux/mman.h
+++ b/include/uapi/linux/mman.h
@@ -4,6 +4,7 @@
#include <asm/mman.h>
#include <asm-generic/hugetlb_encode.h>
+#include <linux/types.h>
#define MREMAP_MAYMOVE 1
#define MREMAP_FIXED 2
@@ -41,4 +42,12 @@
#define MAP_HUGE_2GB HUGETLB_FLAG_ENCODE_2GB
#define MAP_HUGE_16GB HUGETLB_FLAG_ENCODE_16GB
+struct cachestat {
+ __u64 nr_cache;
+ __u64 nr_dirty;
+ __u64 nr_writeback;
+ __u64 nr_evicted;
+ __u64 nr_recently_evicted;
+};
+
#endif /* _UAPI_LINUX_MMAN_H */
diff --git a/init/Kconfig b/init/Kconfig
index 694f7c160c9c..ecc4f781dd6c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1798,6 +1798,16 @@ config RSEQ
If unsure, say Y.
+config CACHESTAT
+ bool "Enable cachestat() system call" if EXPERT
+ default y
+ help
+ Enable the cachestat system call, which queries the page cache
+ statistics of a file (number of cached pages, dirty pages,
+ pages marked for writeback, (recently) evicted pages).
+
+ If unsure say Y here.
+
config DEBUG_RSEQ
default n
bool "Enabled debugging of rseq() system call" if EXPERT
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 860b2dcf3ac4..04bfb1e4d377 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -299,6 +299,7 @@ COND_SYSCALL(set_mempolicy);
COND_SYSCALL(migrate_pages);
COND_SYSCALL(move_pages);
COND_SYSCALL(set_mempolicy_home_node);
+COND_SYSCALL(cachestat);
COND_SYSCALL(perf_event_open);
COND_SYSCALL(accept4);
diff --git a/mm/Makefile b/mm/Makefile
index 8e105e5b3e29..61c9c3f81cef 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -138,3 +138,4 @@ obj-$(CONFIG_IO_MAPPING) += io-mapping.o
obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o
obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
+obj-$(CONFIG_CACHESTAT) += cachestat.o
diff --git a/mm/cachestat.c b/mm/cachestat.c
new file mode 100644
index 000000000000..931f5e37326b
--- /dev/null
+++ b/mm/cachestat.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * The cachestat() system call.
+ */
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/syscalls.h>
+#include <linux/shmem_fs.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <uapi/linux/mman.h>
+
+#include "swap.h"
+
+/*
+ * The cachestat(5) system call.
+ *
+ * cachestat() returns the page cache status of a file in the
+ * bytes specified by `off` and `len`: number of cached pages,
+ * number of dirty pages, number of pages marked for writeback,
+ * number of (recently) evicted pages.
+ *
+ * `off` and `len` must be non-negative integers. If `len` > 0,
+ * the queried range is [`off`, `off` + `len`]. If `len` == 0,
+ * we will query in the range from `off` to the end of the file.
+ *
+ * `cstat_size` allows users to obtain partial results. The syscall
+ * will copy the first `csstat_size` bytes to the specified userspace
+ * memory. It also makes the cachestat struct extensible - new fields
+ * can be added in the future without breaking existing usage.
+ * `cstat_size` must be a non-negative value that is no larger than
+ * the current size of the cachestat struct.
+ *
+ * The `flags` argument is unused for now, but is included for future
+ * extensibility. User should pass 0 (i.e no flag specified).
+ *
+ * Because the status of a page can change after cachestat() checks it
+ * but before it returns to the application, the returned values may
+ * contain stale information.
+ *
+ * return values:
+ * zero - success
+ * -EFAULT - cstat points to an illegal address
+ * -EINVAL - invalid arguments
+ * -EBADF - invalid file descriptor
+ */
+SYSCALL_DEFINE6(cachestat, unsigned int, fd, off_t, off, size_t, len,
+ size_t, cstat_size, struct cachestat __user *, cstat,
+ unsigned int, flags)
+{
+ struct fd f;
+ struct cachestat cs;
+
+ memset(&cs, 0, sizeof(struct cachestat));
+
+ if (off < 0 || cstat_size > sizeof(struct cachestat) || flags != 0)
+ return -EINVAL;
+
+ if (!access_ok(cstat, sizeof(struct cachestat)))
+ return -EFAULT;
+
+ f = fdget(fd);
+ if (f.file) {
+ struct address_space *mapping = f.file->f_mapping;
+ pgoff_t first_index = off >> PAGE_SHIFT;
+ pgoff_t last_index =
+ len == 0 ? ULONG_MAX : (off + len - 1) >> PAGE_SHIFT;
+ XA_STATE(xas, &mapping->i_pages, first_index);
+ struct folio *folio;
+
+ rcu_read_lock();
+ xas_for_each(&xas, folio, last_index) {
+ if (xas_retry(&xas, folio) || !folio)
+ continue;
+
+ if (xa_is_value(folio)) {
+ /* page is evicted */
+ void *shadow = (void *)folio;
+ bool workingset; /* not used */
+
+ cs.nr_evicted += 1;
+
+#ifdef CONFIG_SWAP /* implies CONFIG_MMU */
+ if (shmem_mapping(mapping)) {
+ /* shmem file - in swap cache */
+ swp_entry_t swp = radix_to_swp_entry(folio);
+
+ shadow = get_shadow_from_swap_cache(swp);
+ }
+#endif
+ if (workingset_test_recent(shadow, true, &workingset))
+ cs.nr_recently_evicted += 1;
+
+ continue;
+ }
+
+ /* page is in cache */
+ cs.nr_cache += 1;
+
+ if (folio_test_dirty(folio))
+ cs.nr_dirty += 1;
+
+ if (folio_test_writeback(folio))
+ cs.nr_writeback += 1;
+ }
+ rcu_read_unlock();
+ fdput(f);
+
+ if (copy_to_user(cstat, &cs, cstat_size))
+ return -EFAULT;
+
+ return 0;
+ }
+
+ return -EBADF;
+}
--
2.30.2
Test cachestat on a newly created file, /dev/ files, and /proc/ files.
Signed-off-by: Nhat Pham <[email protected]>
---
MAINTAINERS | 1 +
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/cachestat/.gitignore | 2 +
tools/testing/selftests/cachestat/Makefile | 7 +
.../selftests/cachestat/test_cachestat.c | 186 ++++++++++++++++++
5 files changed, 197 insertions(+)
create mode 100644 tools/testing/selftests/cachestat/.gitignore
create mode 100644 tools/testing/selftests/cachestat/Makefile
create mode 100644 tools/testing/selftests/cachestat/test_cachestat.c
diff --git a/MAINTAINERS b/MAINTAINERS
index baa081a1fe52..1b8bc6151e86 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4558,6 +4558,7 @@ M: Johannes Weiner <[email protected]>
L: [email protected]
S: Maintained
F: mm/cachestat.c
+F: tools/testing/selftests/cachestat/test_cachestat.c
CADENCE MIPI-CSI2 BRIDGES
M: Maxime Ripard <[email protected]>
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 0464b2c6c1e4..3cad0b38c5c2 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -4,6 +4,7 @@ TARGETS += amd-pstate
TARGETS += arm64
TARGETS += bpf
TARGETS += breakpoints
+TARGETS += cachestat
TARGETS += capabilities
TARGETS += cgroup
TARGETS += clone3
diff --git a/tools/testing/selftests/cachestat/.gitignore b/tools/testing/selftests/cachestat/.gitignore
new file mode 100644
index 000000000000..d6c30b43a4bb
--- /dev/null
+++ b/tools/testing/selftests/cachestat/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+test_cachestat
diff --git a/tools/testing/selftests/cachestat/Makefile b/tools/testing/selftests/cachestat/Makefile
new file mode 100644
index 000000000000..04e84fd7d8ce
--- /dev/null
+++ b/tools/testing/selftests/cachestat/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0
+TEST_GEN_PROGS := test_cachestat
+
+CFLAGS += $(KHDR_INCLUDES)
+CFLAGS += -Wall
+
+include ../lib.mk
diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
new file mode 100644
index 000000000000..bb767147d08f
--- /dev/null
+++ b/tools/testing/selftests/cachestat/test_cachestat.c
@@ -0,0 +1,186 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdbool.h>
+#include <linux/kernel.h>
+#include <linux/mman.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <string.h>
+#include <fcntl.h>
+
+#include "../kselftest.h"
+
+static const char * const dev_files[] = {
+ "/dev/zero", "/dev/null", "/dev/urandom",
+ "/proc/version", "/proc"
+};
+
+/*
+ * Open/create the file at filename, (optionally) write random data to it
+ * (exactly num_pages), then test the cachestat syscall on this file.
+ *
+ * If test_fsync == true, fsync the file, then check the number of dirty
+ * pages.
+ */
+bool test_cachestat(const char *filename, bool write_random, bool create,
+ bool test_fsync, int num_pages, int open_flags, mode_t open_mode)
+{
+ int cachestat_nr = 451;
+ size_t PS = sysconf(_SC_PAGESIZE);
+ int filesize = num_pages * PS;
+ bool ret = true;
+ int random_fd;
+ long syscall_ret;
+ struct cachestat cs;
+
+ int fd = open(filename, open_flags, open_mode);
+
+ if (fd == -1) {
+ ksft_print_msg("Unable to create/open file.\n");
+ goto out;
+ } else {
+ ksft_print_msg("Create/open %s\n", filename);
+ }
+
+ if (write_random) {
+ char data[filesize];
+
+ random_fd = open("/dev/urandom", O_RDONLY);
+
+ if (random_fd < 0) {
+ ksft_print_msg("Unable to access urandom.\n");
+ ret = false;
+ goto out1;
+ } else {
+ int remained = filesize;
+ char *cursor = data;
+
+ while (remained) {
+ ssize_t read_len = read(random_fd, cursor, remained);
+
+ if (read_len <= 0) {
+ ksft_print_msg("Unable to read from urandom.\n");
+ ret = false;
+ goto out2;
+ }
+
+ remained -= read_len;
+ cursor += read_len;
+ }
+
+ /* write random data to fd */
+ remained = filesize;
+ cursor = data;
+ while (remained) {
+ ssize_t write_len = write(fd, cursor, remained);
+
+ if (write_len <= 0) {
+ ksft_print_msg("Unable write random data to file.\n");
+ ret = false;
+ goto out2;
+ }
+
+ remained -= write_len;
+ cursor += write_len;
+ }
+ }
+ }
+
+ syscall_ret = syscall(cachestat_nr, fd, 0, filesize,
+ sizeof(struct cachestat), &cs, 0);
+
+ ksft_print_msg("Cachestat call returned %ld\n", syscall_ret);
+
+ if (syscall_ret) {
+ ksft_print_msg("Cachestat returned non-zero.\n");
+ ret = false;
+
+ if (write_random)
+ goto out2;
+ else
+ goto out1;
+
+ } else {
+ ksft_print_msg(
+ "Using cachestat: Cached: %lu, Dirty: %lu, Writeback: %lu, Evicted: %lu, Recently Evicted: %lu\n",
+ cs.nr_cache, cs.nr_dirty, cs.nr_writeback,
+ cs.nr_evicted, cs.nr_recently_evicted);
+
+ if (write_random) {
+ if (cs.nr_cache + cs.nr_evicted != num_pages) {
+ ksft_print_msg(
+ "Total number of cached and evicted pages is off.\n");
+ ret = false;
+ }
+ }
+ }
+
+ if (test_fsync) {
+ if (fsync(fd)) {
+ ksft_print_msg("fsync fails.\n");
+ ret = false;
+ } else {
+ syscall_ret = syscall(cachestat_nr, fd, 0, filesize,
+ sizeof(struct cachestat), &cs, 0);
+
+ ksft_print_msg("Cachestat call (after fsync) returned %ld\n",
+ syscall_ret);
+
+ if (!syscall_ret) {
+ ksft_print_msg(
+ "Using cachestat: Cached: %lu, Dirty: %lu, Writeback: %lu, Evicted: %lu, Recently Evicted: %lu\n",
+ cs.nr_cache, cs.nr_dirty, cs.nr_writeback,
+ cs.nr_evicted, cs.nr_recently_evicted);
+
+ if (cs.nr_dirty) {
+ ret = false;
+ ksft_print_msg(
+ "Number of dirty should be zero after fsync.\n");
+ }
+ } else {
+ ksft_print_msg("Cachestat (after fsync) returned non-zero.\n");
+ ret = false;
+
+ if (write_random)
+ goto out2;
+ else
+ goto out1;
+ }
+ }
+ }
+
+out2:
+ if (write_random)
+ close(random_fd);
+out1:
+ close(fd);
+
+ if (create)
+ remove(filename);
+out:
+ return ret;
+}
+
+int main(void)
+{
+ for (int i = 0; i < 5; i++) {
+ const char *dev_filename = dev_files[i];
+
+ if (test_cachestat(dev_filename, false, false, false,
+ 4, O_RDONLY, 0400))
+ ksft_test_result_pass("cachestat works with %s\n", dev_filename);
+ else
+ ksft_test_result_fail("cachestat fails with %s\n", dev_filename);
+ }
+
+ if (test_cachestat("tmpfilecachestat", true, true,
+ true, 4, O_CREAT | O_RDWR, 0400 | 0600))
+ ksft_test_result_pass("cachestat works with a normal file\n");
+ else
+ ksft_test_result_fail("cachestat fails with normal file\n");
+
+ return 0;
+}
--
2.30.2
Implement a new syscall that queries cache state of a file and
summarizes the number of cached pages, number of dirty pages, number of
pages marked for writeback, number of (recently) evicted pages, etc. in
a given range.
NAME
cachestat - query the page cache status of a file.
SYNOPSIS
#include <sys/mman.h>
struct cachestat {
__u64 nr_cache;
__u64 nr_dirty;
__u64 nr_writeback;
__u64 nr_evicted;
__u64 nr_recently_evicted;
};
int cachestat(unsigned int fd, off_t off, size_t len,
size_t cstat_size, struct cachestat *cstat,
unsigned int flags);
DESCRIPTION
cachestat() queries the number of cached pages, number of dirty
pages, number of pages marked for writeback, number of (recently)
evicted pages, in the bytes range given by `off` and `len`.
These values are returned in a cachestat struct, whose address is
given by the `cstat` argument.
The `off` and `len` arguments must be non-negative integers. If
`len` > 0, the queried range is [`off`, `off` + `len`]. If `len` ==
0, we will query in the range from `off` to the end of the file.
`cstat_size` allows users to obtain partial results. The syscall
will copy the first `csstat_size` bytes to the specified userspace
memory. `cstat_size` must be a non-negative value that is no larger
than the current size of the cachestat struct.
The `flags` argument is unused for now, but is included for future
extensibility. User should pass 0 (i.e no flag specified).
RETURN VALUE
On success, cachestat returns 0. On error, -1 is returned, and errno
is set to indicate the error.
ERRORS
EFAULT cstat points to an invalid address.
EINVAL invalid `cstat_size` or `flags`
EBADF invalid file descriptor.
Signed-off-by: Nhat Pham <[email protected]>
---
MAINTAINERS | 7 ++
arch/alpha/kernel/syscalls/syscall.tbl | 1 +
arch/arm/tools/syscall.tbl | 1 +
arch/ia64/kernel/syscalls/syscall.tbl | 1 +
arch/m68k/kernel/syscalls/syscall.tbl | 1 +
arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
arch/parisc/kernel/syscalls/syscall.tbl | 1 +
arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
arch/s390/kernel/syscalls/syscall.tbl | 1 +
arch/sh/kernel/syscalls/syscall.tbl | 1 +
arch/sparc/kernel/syscalls/syscall.tbl | 1 +
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
include/linux/syscalls.h | 3 +
include/uapi/asm-generic/unistd.h | 5 +-
include/uapi/linux/mman.h | 9 ++
init/Kconfig | 10 ++
kernel/sys_ni.c | 1 +
mm/Makefile | 1 +
mm/cachestat.c | 117 ++++++++++++++++++++
21 files changed, 165 insertions(+), 1 deletion(-)
create mode 100644 mm/cachestat.c
diff --git a/MAINTAINERS b/MAINTAINERS
index a198da986146..baa081a1fe52 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4552,6 +4552,13 @@ S: Supported
F: Documentation/filesystems/caching/cachefiles.rst
F: fs/cachefiles/
+CACHESTAT: PAGE CACHE STATS FOR A FILE
+M: Nhat Pham <[email protected]>
+M: Johannes Weiner <[email protected]>
+L: [email protected]
+S: Maintained
+F: mm/cachestat.c
+
CADENCE MIPI-CSI2 BRIDGES
M: Maxime Ripard <[email protected]>
L: [email protected]
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 8ebacf37a8cf..1f13995d00d7 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -490,3 +490,4 @@
558 common process_mrelease sys_process_mrelease
559 common futex_waitv sys_futex_waitv
560 common set_mempolicy_home_node sys_ni_syscall
+561 common cachestat sys_cachestat
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index ac964612d8b0..8ebed8a13874 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -464,3 +464,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index 72c929d9902b..f8c74ffeeefb 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -371,3 +371,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index b1f3940bc298..4f504783371f 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -450,3 +450,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 820145e47350..858d22bf275c 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -456,3 +456,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index 8a99c998da9b..7c84a72306d1 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -448,3 +448,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 2bca64f96164..937460f0a8ec 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -530,3 +530,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 nospu set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 799147658dee..7df0329d46cb 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -453,3 +453,4 @@
448 common process_mrelease sys_process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat sys_cachestat
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 2de85c977f54..97377e8c5025 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -453,3 +453,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 4398cc6fb68d..faa835f3c54a 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -496,3 +496,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 320480a8db4f..bc0a3c941b35 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -455,3 +455,4 @@
448 i386 process_mrelease sys_process_mrelease
449 i386 futex_waitv sys_futex_waitv
450 i386 set_mempolicy_home_node sys_set_mempolicy_home_node
+451 i386 cachestat sys_cachestat
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index c84d12608cd2..8eed4cdc7965 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -372,6 +372,7 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
#
# Due to a historical design error, certain syscalls are numbered differently
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 52c94ab5c205..2b69c3c035b6 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -421,3 +421,4 @@
448 common process_mrelease sys_process_mrelease
449 common futex_waitv sys_futex_waitv
450 common set_mempolicy_home_node sys_set_mempolicy_home_node
+451 common cachestat sys_cachestat
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a34b0f9a9972..50f8c6999d99 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -72,6 +72,7 @@ struct open_how;
struct mount_attr;
struct landlock_ruleset_attr;
enum landlock_rule_type;
+struct cachestat;
#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -1056,6 +1057,8 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
unsigned long home_node,
unsigned long flags);
+asmlinkage long sys_cachestat(unsigned int fd, off_t off, size_t len,
+ size_t cstat_size, struct cachestat __user *cstat, unsigned int flags);
/*
* Architecture-specific system calls
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 45fa180cc56a..cd639fae9086 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
#define __NR_set_mempolicy_home_node 450
__SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
+#define __NR_cachestat 451
+__SYSCALL(__NR_cachestat, sys_cachestat)
+
#undef __NR_syscalls
-#define __NR_syscalls 451
+#define __NR_syscalls 452
/*
* 32 bit systems traditionally used different
diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
index f55bc680b5b0..fe03ed0b7587 100644
--- a/include/uapi/linux/mman.h
+++ b/include/uapi/linux/mman.h
@@ -4,6 +4,7 @@
#include <asm/mman.h>
#include <asm-generic/hugetlb_encode.h>
+#include <linux/types.h>
#define MREMAP_MAYMOVE 1
#define MREMAP_FIXED 2
@@ -41,4 +42,12 @@
#define MAP_HUGE_2GB HUGETLB_FLAG_ENCODE_2GB
#define MAP_HUGE_16GB HUGETLB_FLAG_ENCODE_16GB
+struct cachestat {
+ __u64 nr_cache;
+ __u64 nr_dirty;
+ __u64 nr_writeback;
+ __u64 nr_evicted;
+ __u64 nr_recently_evicted;
+};
+
#endif /* _UAPI_LINUX_MMAN_H */
diff --git a/init/Kconfig b/init/Kconfig
index 694f7c160c9c..ecc4f781dd6c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1798,6 +1798,16 @@ config RSEQ
If unsure, say Y.
+config CACHESTAT
+ bool "Enable cachestat() system call" if EXPERT
+ default y
+ help
+ Enable the cachestat system call, which queries the page cache
+ statistics of a file (number of cached pages, dirty pages,
+ pages marked for writeback, (recently) evicted pages).
+
+ If unsure say Y here.
+
config DEBUG_RSEQ
default n
bool "Enabled debugging of rseq() system call" if EXPERT
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 860b2dcf3ac4..04bfb1e4d377 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -299,6 +299,7 @@ COND_SYSCALL(set_mempolicy);
COND_SYSCALL(migrate_pages);
COND_SYSCALL(move_pages);
COND_SYSCALL(set_mempolicy_home_node);
+COND_SYSCALL(cachestat);
COND_SYSCALL(perf_event_open);
COND_SYSCALL(accept4);
diff --git a/mm/Makefile b/mm/Makefile
index 8e105e5b3e29..61c9c3f81cef 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -138,3 +138,4 @@ obj-$(CONFIG_IO_MAPPING) += io-mapping.o
obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o
obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
+obj-$(CONFIG_CACHESTAT) += cachestat.o
diff --git a/mm/cachestat.c b/mm/cachestat.c
new file mode 100644
index 000000000000..254678172726
--- /dev/null
+++ b/mm/cachestat.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * The cachestat() system call.
+ */
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/syscalls.h>
+#include <linux/shmem_fs.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <uapi/linux/mman.h>
+
+#include "swap.h"
+
+/*
+ * The cachestat(5) system call.
+ *
+ * cachestat() returns the page cache status of a file in the
+ * bytes specified by `off` and `len`: number of cached pages,
+ * number of dirty pages, number of pages marked for writeback,
+ * number of (recently) evicted pages.
+ *
+ * `off` and `len` must be non-negative integers. If `len` > 0,
+ * the queried range is [`off`, `off` + `len`]. If `len` == 0,
+ * we will query in the range from `off` to the end of the file.
+ *
+ * `cstat_size` allows users to obtain partial results. The syscall
+ * will copy the first `csstat_size` bytes to the specified userspace
+ * memory. It also makes the cachestat struct extensible - new fields
+ * can be added in the future without breaking existing usage.
+ * `cstat_size` must be a non-negative value that is no larger than
+ * the current size of the cachestat struct.
+ *
+ * The `flags` argument is unused for now, but is included for future
+ * extensibility. User should pass 0 (i.e no flag specified).
+ *
+ * Because the status of a page can change after cachestat() checks it
+ * but before it returns to the application, the returned values may
+ * contain stale information.
+ *
+ * return values:
+ * zero - success
+ * -EFAULT - cstat points to an illegal address
+ * -EINVAL - invalid arguments
+ * -EBADF - invalid file descriptor
+ */
+SYSCALL_DEFINE6(cachestat, unsigned int, fd, off_t, off, size_t, len,
+ size_t, cstat_size, struct cachestat __user *, cstat,
+ unsigned int, flags)
+{
+ struct fd f;
+ struct cachestat cs;
+
+ memset(&cs, 0, sizeof(struct cachestat));
+
+ if (off < 0 || cstat_size > sizeof(struct cachestat) || flags != 0)
+ return -EINVAL;
+
+ if (!access_ok(cstat, cstat_size))
+ return -EFAULT;
+
+ f = fdget(fd);
+ if (f.file) {
+ struct address_space *mapping = f.file->f_mapping;
+ pgoff_t first_index = off >> PAGE_SHIFT;
+ pgoff_t last_index =
+ len == 0 ? ULONG_MAX : (off + len - 1) >> PAGE_SHIFT;
+ XA_STATE(xas, &mapping->i_pages, first_index);
+ struct folio *folio;
+
+ rcu_read_lock();
+ xas_for_each(&xas, folio, last_index) {
+ if (xas_retry(&xas, folio) || !folio)
+ continue;
+
+ if (xa_is_value(folio)) {
+ /* page is evicted */
+ void *shadow = (void *)folio;
+ bool workingset; /* not used */
+
+ cs.nr_evicted += 1;
+
+#ifdef CONFIG_SWAP /* implies CONFIG_MMU */
+ if (shmem_mapping(mapping)) {
+ /* shmem file - in swap cache */
+ swp_entry_t swp = radix_to_swp_entry(folio);
+
+ shadow = get_shadow_from_swap_cache(swp);
+ }
+#endif
+ if (workingset_test_recent(shadow, true, &workingset))
+ cs.nr_recently_evicted += 1;
+
+ continue;
+ }
+
+ /* page is in cache */
+ cs.nr_cache += 1;
+
+ if (folio_test_dirty(folio))
+ cs.nr_dirty += 1;
+
+ if (folio_test_writeback(folio))
+ cs.nr_writeback += 1;
+ }
+ rcu_read_unlock();
+ fdput(f);
+
+ if (copy_to_user(cstat, &cs, cstat_size))
+ return -EFAULT;
+
+ return 0;
+ }
+
+ return -EBADF;
+}
--
2.30.2
On Thu, Dec 8, 2022 at 12:28 PM Nhat Pham <[email protected]> wrote:
>
> Implement a new syscall that queries cache state of a file and
> summarizes the number of cached pages, number of dirty pages, number of
> pages marked for writeback, number of (recently) evicted pages, etc. in
> a given range.
>
> NAME
> cachestat - query the page cache status of a file.
>
> SYNOPSIS
> #include <sys/mman.h>
>
> struct cachestat {
> __u64 nr_cache;
> __u64 nr_dirty;
> __u64 nr_writeback;
> __u64 nr_evicted;
> __u64 nr_recently_evicted;
> };
>
> int cachestat(unsigned int fd, off_t off, size_t len,
> size_t cstat_size, struct cachestat *cstat,
> unsigned int flags);
>
> DESCRIPTION
> cachestat() queries the number of cached pages, number of dirty
> pages, number of pages marked for writeback, number of (recently)
> evicted pages, in the bytes range given by `off` and `len`.
>
> These values are returned in a cachestat struct, whose address is
> given by the `cstat` argument.
>
> The `off` and `len` arguments must be non-negative integers. If
> `len` > 0, the queried range is [`off`, `off` + `len`]. If `len` ==
> 0, we will query in the range from `off` to the end of the file.
>
> `cstat_size` allows users to obtain partial results. The syscall
> will copy the first `csstat_size` bytes to the specified userspace
> memory. `cstat_size` must be a non-negative value that is no larger
> than the current size of the cachestat struct.
>
> The `flags` argument is unused for now, but is included for future
> extensibility. User should pass 0 (i.e no flag specified).
>
> RETURN VALUE
> On success, cachestat returns 0. On error, -1 is returned, and errno
> is set to indicate the error.
>
> ERRORS
> EFAULT cstat points to an invalid address.
>
> EINVAL invalid `cstat_size` or `flags`
>
> EBADF invalid file descriptor.
>
> Signed-off-by: Nhat Pham <[email protected]>
> ---
> MAINTAINERS | 7 ++
> arch/alpha/kernel/syscalls/syscall.tbl | 1 +
> arch/arm/tools/syscall.tbl | 1 +
> arch/ia64/kernel/syscalls/syscall.tbl | 1 +
> arch/m68k/kernel/syscalls/syscall.tbl | 1 +
> arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
> arch/parisc/kernel/syscalls/syscall.tbl | 1 +
> arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
> arch/s390/kernel/syscalls/syscall.tbl | 1 +
> arch/sh/kernel/syscalls/syscall.tbl | 1 +
> arch/sparc/kernel/syscalls/syscall.tbl | 1 +
> arch/x86/entry/syscalls/syscall_32.tbl | 1 +
> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
> include/linux/syscalls.h | 3 +
> include/uapi/asm-generic/unistd.h | 5 +-
> include/uapi/linux/mman.h | 9 ++
> init/Kconfig | 10 ++
> kernel/sys_ni.c | 1 +
> mm/Makefile | 1 +
> mm/cachestat.c | 117 ++++++++++++++++++++
> 21 files changed, 165 insertions(+), 1 deletion(-)
> create mode 100644 mm/cachestat.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a198da986146..baa081a1fe52 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4552,6 +4552,13 @@ S: Supported
> F: Documentation/filesystems/caching/cachefiles.rst
> F: fs/cachefiles/
>
> +CACHESTAT: PAGE CACHE STATS FOR A FILE
> +M: Nhat Pham <[email protected]>
> +M: Johannes Weiner <[email protected]>
> +L: [email protected]
> +S: Maintained
> +F: mm/cachestat.c
> +
> CADENCE MIPI-CSI2 BRIDGES
> M: Maxime Ripard <[email protected]>
> L: [email protected]
> diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
> index 8ebacf37a8cf..1f13995d00d7 100644
> --- a/arch/alpha/kernel/syscalls/syscall.tbl
> +++ b/arch/alpha/kernel/syscalls/syscall.tbl
> @@ -490,3 +490,4 @@
> 558 common process_mrelease sys_process_mrelease
> 559 common futex_waitv sys_futex_waitv
> 560 common set_mempolicy_home_node sys_ni_syscall
> +561 common cachestat sys_cachestat
> diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
> index ac964612d8b0..8ebed8a13874 100644
> --- a/arch/arm/tools/syscall.tbl
> +++ b/arch/arm/tools/syscall.tbl
> @@ -464,3 +464,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
> index 72c929d9902b..f8c74ffeeefb 100644
> --- a/arch/ia64/kernel/syscalls/syscall.tbl
> +++ b/arch/ia64/kernel/syscalls/syscall.tbl
> @@ -371,3 +371,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
> index b1f3940bc298..4f504783371f 100644
> --- a/arch/m68k/kernel/syscalls/syscall.tbl
> +++ b/arch/m68k/kernel/syscalls/syscall.tbl
> @@ -450,3 +450,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
> index 820145e47350..858d22bf275c 100644
> --- a/arch/microblaze/kernel/syscalls/syscall.tbl
> +++ b/arch/microblaze/kernel/syscalls/syscall.tbl
> @@ -456,3 +456,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
> index 8a99c998da9b..7c84a72306d1 100644
> --- a/arch/parisc/kernel/syscalls/syscall.tbl
> +++ b/arch/parisc/kernel/syscalls/syscall.tbl
> @@ -448,3 +448,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> index 2bca64f96164..937460f0a8ec 100644
> --- a/arch/powerpc/kernel/syscalls/syscall.tbl
> +++ b/arch/powerpc/kernel/syscalls/syscall.tbl
> @@ -530,3 +530,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 nospu set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
> index 799147658dee..7df0329d46cb 100644
> --- a/arch/s390/kernel/syscalls/syscall.tbl
> +++ b/arch/s390/kernel/syscalls/syscall.tbl
> @@ -453,3 +453,4 @@
> 448 common process_mrelease sys_process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat sys_cachestat
> diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
> index 2de85c977f54..97377e8c5025 100644
> --- a/arch/sh/kernel/syscalls/syscall.tbl
> +++ b/arch/sh/kernel/syscalls/syscall.tbl
> @@ -453,3 +453,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
> index 4398cc6fb68d..faa835f3c54a 100644
> --- a/arch/sparc/kernel/syscalls/syscall.tbl
> +++ b/arch/sparc/kernel/syscalls/syscall.tbl
> @@ -496,3 +496,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index 320480a8db4f..bc0a3c941b35 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -455,3 +455,4 @@
> 448 i386 process_mrelease sys_process_mrelease
> 449 i386 futex_waitv sys_futex_waitv
> 450 i386 set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 i386 cachestat sys_cachestat
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index c84d12608cd2..8eed4cdc7965 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -372,6 +372,7 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
>
> #
> # Due to a historical design error, certain syscalls are numbered differently
> diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
> index 52c94ab5c205..2b69c3c035b6 100644
> --- a/arch/xtensa/kernel/syscalls/syscall.tbl
> +++ b/arch/xtensa/kernel/syscalls/syscall.tbl
> @@ -421,3 +421,4 @@
> 448 common process_mrelease sys_process_mrelease
> 449 common futex_waitv sys_futex_waitv
> 450 common set_mempolicy_home_node sys_set_mempolicy_home_node
> +451 common cachestat sys_cachestat
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index a34b0f9a9972..50f8c6999d99 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -72,6 +72,7 @@ struct open_how;
> struct mount_attr;
> struct landlock_ruleset_attr;
> enum landlock_rule_type;
> +struct cachestat;
>
> #include <linux/types.h>
> #include <linux/aio_abi.h>
> @@ -1056,6 +1057,8 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
> asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
> unsigned long home_node,
> unsigned long flags);
> +asmlinkage long sys_cachestat(unsigned int fd, off_t off, size_t len,
> + size_t cstat_size, struct cachestat __user *cstat, unsigned int flags);
>
> /*
> * Architecture-specific system calls
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index 45fa180cc56a..cd639fae9086 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
> #define __NR_set_mempolicy_home_node 450
> __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
>
> +#define __NR_cachestat 451
> +__SYSCALL(__NR_cachestat, sys_cachestat)
> +
> #undef __NR_syscalls
> -#define __NR_syscalls 451
> +#define __NR_syscalls 452
>
> /*
> * 32 bit systems traditionally used different
> diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
> index f55bc680b5b0..fe03ed0b7587 100644
> --- a/include/uapi/linux/mman.h
> +++ b/include/uapi/linux/mman.h
> @@ -4,6 +4,7 @@
>
> #include <asm/mman.h>
> #include <asm-generic/hugetlb_encode.h>
> +#include <linux/types.h>
>
> #define MREMAP_MAYMOVE 1
> #define MREMAP_FIXED 2
> @@ -41,4 +42,12 @@
> #define MAP_HUGE_2GB HUGETLB_FLAG_ENCODE_2GB
> #define MAP_HUGE_16GB HUGETLB_FLAG_ENCODE_16GB
>
> +struct cachestat {
> + __u64 nr_cache;
> + __u64 nr_dirty;
> + __u64 nr_writeback;
> + __u64 nr_evicted;
> + __u64 nr_recently_evicted;
> +};
> +
> #endif /* _UAPI_LINUX_MMAN_H */
> diff --git a/init/Kconfig b/init/Kconfig
> index 694f7c160c9c..ecc4f781dd6c 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1798,6 +1798,16 @@ config RSEQ
>
> If unsure, say Y.
>
> +config CACHESTAT
> + bool "Enable cachestat() system call" if EXPERT
> + default y
> + help
> + Enable the cachestat system call, which queries the page cache
> + statistics of a file (number of cached pages, dirty pages,
> + pages marked for writeback, (recently) evicted pages).
> +
> + If unsure say Y here.
> +
> config DEBUG_RSEQ
> default n
> bool "Enabled debugging of rseq() system call" if EXPERT
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 860b2dcf3ac4..04bfb1e4d377 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -299,6 +299,7 @@ COND_SYSCALL(set_mempolicy);
> COND_SYSCALL(migrate_pages);
> COND_SYSCALL(move_pages);
> COND_SYSCALL(set_mempolicy_home_node);
> +COND_SYSCALL(cachestat);
>
> COND_SYSCALL(perf_event_open);
> COND_SYSCALL(accept4);
> diff --git a/mm/Makefile b/mm/Makefile
> index 8e105e5b3e29..61c9c3f81cef 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -138,3 +138,4 @@ obj-$(CONFIG_IO_MAPPING) += io-mapping.o
> obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
> obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o
> obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
> +obj-$(CONFIG_CACHESTAT) += cachestat.o
> diff --git a/mm/cachestat.c b/mm/cachestat.c
> new file mode 100644
> index 000000000000..931f5e37326b
> --- /dev/null
> +++ b/mm/cachestat.c
> @@ -0,0 +1,117 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
> +/*
> + * The cachestat() system call.
> + */
> +#include <linux/file.h>
> +#include <linux/fs.h>
> +#include <linux/syscalls.h>
> +#include <linux/shmem_fs.h>
> +#include <linux/swap.h>
> +#include <linux/swapops.h>
> +#include <uapi/linux/mman.h>
> +
> +#include "swap.h"
> +
> +/*
> + * The cachestat(5) system call.
> + *
> + * cachestat() returns the page cache status of a file in the
> + * bytes specified by `off` and `len`: number of cached pages,
> + * number of dirty pages, number of pages marked for writeback,
> + * number of (recently) evicted pages.
> + *
> + * `off` and `len` must be non-negative integers. If `len` > 0,
> + * the queried range is [`off`, `off` + `len`]. If `len` == 0,
> + * we will query in the range from `off` to the end of the file.
> + *
> + * `cstat_size` allows users to obtain partial results. The syscall
> + * will copy the first `csstat_size` bytes to the specified userspace
> + * memory. It also makes the cachestat struct extensible - new fields
> + * can be added in the future without breaking existing usage.
> + * `cstat_size` must be a non-negative value that is no larger than
> + * the current size of the cachestat struct.
> + *
> + * The `flags` argument is unused for now, but is included for future
> + * extensibility. User should pass 0 (i.e no flag specified).
> + *
> + * Because the status of a page can change after cachestat() checks it
> + * but before it returns to the application, the returned values may
> + * contain stale information.
> + *
> + * return values:
> + * zero - success
> + * -EFAULT - cstat points to an illegal address
> + * -EINVAL - invalid arguments
> + * -EBADF - invalid file descriptor
> + */
> +SYSCALL_DEFINE6(cachestat, unsigned int, fd, off_t, off, size_t, len,
> + size_t, cstat_size, struct cachestat __user *, cstat,
> + unsigned int, flags)
> +{
> + struct fd f;
> + struct cachestat cs;
> +
> + memset(&cs, 0, sizeof(struct cachestat));
> +
> + if (off < 0 || cstat_size > sizeof(struct cachestat) || flags != 0)
> + return -EINVAL;
> +
> + if (!access_ok(cstat, sizeof(struct cachestat)))
> + return -EFAULT;
Oops, this part should really be:
if (!access_ok(cstat, cstat_size))
I'll send a new version of patch 3/4 to fix this...
Hi Nhat,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on shuah-kselftest/next]
[also build test ERROR on shuah-kselftest/fixes tip/x86/asm akpm-mm/mm-everything linus/master v6.1-rc8 next-20221208]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/cachestat-a-new-syscall-for-page-cache-state-of-files/20221209-042856
base: https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git next
patch link: https://lore.kernel.org/r/20221208202808.908690-3-nphamcs%40gmail.com
patch subject: [PATCH v3 2/4] workingset: refactor LRU refault to expose refault recency check
config: hexagon-randconfig-r045-20221207
compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 6e4cea55f0d1104408b26ac574566a0e4de48036)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/e2f34321a236f2cbe1ece4eda8c0aaadaa182739
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Nhat-Pham/cachestat-a-new-syscall-for-page-cache-state-of-files/20221209-042856
git checkout e2f34321a236f2cbe1ece4eda8c0aaadaa182739
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[email protected]>
All errors (new ones prefixed by >>):
In file included from mm/workingset.c:8:
In file included from include/linux/memcontrol.h:13:
In file included from include/linux/cgroup.h:26:
In file included from include/linux/kernel_stat.h:9:
In file included from include/linux/interrupt.h:11:
In file included from include/linux/hardirq.h:11:
In file included from ./arch/hexagon/include/generated/asm/hardirq.h:1:
In file included from include/asm-generic/hardirq.h:17:
In file included from include/linux/irq.h:20:
In file included from include/linux/io.h:13:
In file included from arch/hexagon/include/asm/io.h:334:
include/asm-generic/io.h:547:31: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __raw_readb(PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:560:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __le16_to_cpu((__le16 __force)__raw_readw(PCI_IOBASE + addr));
~~~~~~~~~~ ^
include/uapi/linux/byteorder/little_endian.h:37:51: note: expanded from macro '__le16_to_cpu'
#define __le16_to_cpu(x) ((__force __u16)(__le16)(x))
^
In file included from mm/workingset.c:8:
In file included from include/linux/memcontrol.h:13:
In file included from include/linux/cgroup.h:26:
In file included from include/linux/kernel_stat.h:9:
In file included from include/linux/interrupt.h:11:
In file included from include/linux/hardirq.h:11:
In file included from ./arch/hexagon/include/generated/asm/hardirq.h:1:
In file included from include/asm-generic/hardirq.h:17:
In file included from include/linux/irq.h:20:
In file included from include/linux/io.h:13:
In file included from arch/hexagon/include/asm/io.h:334:
include/asm-generic/io.h:573:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
~~~~~~~~~~ ^
include/uapi/linux/byteorder/little_endian.h:35:51: note: expanded from macro '__le32_to_cpu'
#define __le32_to_cpu(x) ((__force __u32)(__le32)(x))
^
In file included from mm/workingset.c:8:
In file included from include/linux/memcontrol.h:13:
In file included from include/linux/cgroup.h:26:
In file included from include/linux/kernel_stat.h:9:
In file included from include/linux/interrupt.h:11:
In file included from include/linux/hardirq.h:11:
In file included from ./arch/hexagon/include/generated/asm/hardirq.h:1:
In file included from include/asm-generic/hardirq.h:17:
In file included from include/linux/irq.h:20:
In file included from include/linux/io.h:13:
In file included from arch/hexagon/include/asm/io.h:334:
include/asm-generic/io.h:584:33: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writeb(value, PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:594:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:604:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
~~~~~~~~~~ ^
>> mm/workingset.c:265:38: error: indirection requires pointer operand ('int' invalid)
eviction_memcg = mem_cgroup_from_id(*memcgid);
^~~~~~~~
>> mm/workingset.c:267:45: error: passing 'struct pglist_data' to parameter of incompatible type 'struct pglist_data *'; remove *
lruvec = mem_cgroup_lruvec(eviction_memcg, *pgdat);
^~~~~~
include/linux/memcontrol.h:709:33: note: passing argument to parameter 'pgdat' here
struct pglist_data *pgdat)
^
>> mm/workingset.c:271:12: error: indirection requires pointer operand ('unsigned long' invalid)
return !((*token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)));
^~~~~~
6 warnings and 3 errors generated.
vim +265 mm/workingset.c
246
247 /*
248 * Test if the folio is recently evicted.
249 *
250 * As a side effect, also populates the references with
251 * values unpacked from the shadow of the evicted folio.
252 */
253 static bool lru_gen_test_recent(void *shadow, bool file, bool *workingset)
254 {
255 struct mem_cgroup *eviction_memcg;
256 struct lruvec *lruvec;
257 struct lru_gen_struct *lrugen;
258 unsigned long min_seq;
259
260 int memcgid;
261 struct pglist_data *pgdat;
262 unsigned long token;
263
264 unpack_shadow(shadow, &memcgid, &pgdat, &token, workingset);
> 265 eviction_memcg = mem_cgroup_from_id(*memcgid);
266
> 267 lruvec = mem_cgroup_lruvec(eviction_memcg, *pgdat);
268 lrugen = &lruvec->lrugen;
269
270 min_seq = READ_ONCE(lrugen->min_seq[file]);
> 271 return !((*token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)));
272 }
273
--
0-DAY CI Kernel Test Service
https://01.org/lkp
Hi Nhat,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on shuah-kselftest/next]
[also build test ERROR on shuah-kselftest/fixes tip/x86/asm akpm-mm/mm-everything linus/master v6.1-rc8 next-20221208]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/cachestat-a-new-syscall-for-page-cache-state-of-files/20221209-042856
base: https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git next
patch link: https://lore.kernel.org/r/20221208202808.908690-3-nphamcs%40gmail.com
patch subject: [PATCH v3 2/4] workingset: refactor LRU refault to expose refault recency check
config: nios2-randconfig-r001-20221207
compiler: nios2-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/e2f34321a236f2cbe1ece4eda8c0aaadaa182739
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Nhat-Pham/cachestat-a-new-syscall-for-page-cache-state-of-files/20221209-042856
git checkout e2f34321a236f2cbe1ece4eda8c0aaadaa182739
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=nios2 SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[email protected]>
All errors (new ones prefixed by >>):
mm/workingset.c: In function 'lru_gen_test_recent':
>> mm/workingset.c:265:45: error: invalid type argument of unary '*' (have 'int')
265 | eviction_memcg = mem_cgroup_from_id(*memcgid);
| ^~~~~~~~
>> mm/workingset.c:267:52: error: incompatible type for argument 2 of 'mem_cgroup_lruvec'
267 | lruvec = mem_cgroup_lruvec(eviction_memcg, *pgdat);
| ^~~~~~
| |
| struct pglist_data
In file included from mm/workingset.c:8:
include/linux/memcontrol.h:1251:68: note: expected 'struct pglist_data *' but argument is of type 'struct pglist_data'
1251 | struct pglist_data *pgdat)
| ~~~~~~~~~~~~~~~~~~~~^~~~~
>> mm/workingset.c:271:19: error: invalid type argument of unary '*' (have 'long unsigned int')
271 | return !((*token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)));
| ^~~~~~
mm/workingset.c:272:1: error: control reaches end of non-void function [-Werror=return-type]
272 | }
| ^
cc1: some warnings being treated as errors
vim +265 mm/workingset.c
246
247 /*
248 * Test if the folio is recently evicted.
249 *
250 * As a side effect, also populates the references with
251 * values unpacked from the shadow of the evicted folio.
252 */
253 static bool lru_gen_test_recent(void *shadow, bool file, bool *workingset)
254 {
255 struct mem_cgroup *eviction_memcg;
256 struct lruvec *lruvec;
257 struct lru_gen_struct *lrugen;
258 unsigned long min_seq;
259
260 int memcgid;
261 struct pglist_data *pgdat;
262 unsigned long token;
263
264 unpack_shadow(shadow, &memcgid, &pgdat, &token, workingset);
> 265 eviction_memcg = mem_cgroup_from_id(*memcgid);
266
> 267 lruvec = mem_cgroup_lruvec(eviction_memcg, *pgdat);
268 lrugen = &lruvec->lrugen;
269
270 min_seq = READ_ONCE(lrugen->min_seq[file]);
> 271 return !((*token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)));
272 }
273
--
0-DAY CI Kernel Test Service
https://01.org/lkp
In preparation for computing recently evicted pages in cachestat,
refactor workingset_refault and lru_gen_refault to expose a helper
function that would test if an evicted page is recently evicted.
Signed-off-by: Nhat Pham <[email protected]>
---
include/linux/swap.h | 1 +
mm/workingset.c | 129 ++++++++++++++++++++++++++++++-------------
2 files changed, 92 insertions(+), 38 deletions(-)
Fix the issue reported by kernel test robot <[email protected]>
diff --git a/include/linux/swap.h b/include/linux/swap.h
index a18cf4b7c724..dae6f6f955eb 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -361,6 +361,7 @@ static inline void folio_set_swap_entry(struct folio *folio, swp_entry_t entry)
}
/* linux/mm/workingset.c */
+bool workingset_test_recent(void *shadow, bool file, bool *workingset);
void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages);
void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg);
void workingset_refault(struct folio *folio, void *shadow);
diff --git a/mm/workingset.c b/mm/workingset.c
index 79585d55c45d..006482c4e0bd 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -244,6 +244,33 @@ static void *lru_gen_eviction(struct folio *folio)
return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
}
+/*
+ * Test if the folio is recently evicted.
+ *
+ * As a side effect, also populates the references with
+ * values unpacked from the shadow of the evicted folio.
+ */
+static bool lru_gen_test_recent(void *shadow, bool file, bool *workingset)
+{
+ struct mem_cgroup *eviction_memcg;
+ struct lruvec *lruvec;
+ struct lru_gen_struct *lrugen;
+ unsigned long min_seq;
+
+ int memcgid;
+ struct pglist_data *pgdat;
+ unsigned long token;
+
+ unpack_shadow(shadow, &memcgid, &pgdat, &token, workingset);
+ eviction_memcg = mem_cgroup_from_id(memcgid);
+
+ lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
+ lrugen = &lruvec->lrugen;
+
+ min_seq = READ_ONCE(lrugen->min_seq[file]);
+ return !((token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)));
+}
+
static void lru_gen_refault(struct folio *folio, void *shadow)
{
int hist, tier, refs;
@@ -306,6 +333,11 @@ static void *lru_gen_eviction(struct folio *folio)
return NULL;
}
+static bool lru_gen_test_recent(void *shadow, bool file, bool *workingset)
+{
+ return true;
+}
+
static void lru_gen_refault(struct folio *folio, void *shadow)
{
}
@@ -373,40 +405,31 @@ void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
folio_test_workingset(folio));
}
-/**
- * workingset_refault - Evaluate the refault of a previously evicted folio.
- * @folio: The freshly allocated replacement folio.
- * @shadow: Shadow entry of the evicted folio.
+/*
+ * Test if the folio is recently evicted by checking if
+ * refault distance of shadow exceeds workingset size.
*
- * Calculates and evaluates the refault distance of the previously
- * evicted folio in the context of the node and the memcg whose memory
- * pressure caused the eviction.
+ * As a side effect, populate workingset with the value
+ * unpacked from shadow.
*/
-void workingset_refault(struct folio *folio, void *shadow)
+bool workingset_test_recent(void *shadow, bool file, bool *workingset)
{
- bool file = folio_is_file_lru(folio);
struct mem_cgroup *eviction_memcg;
struct lruvec *eviction_lruvec;
unsigned long refault_distance;
unsigned long workingset_size;
- struct pglist_data *pgdat;
- struct mem_cgroup *memcg;
- unsigned long eviction;
- struct lruvec *lruvec;
unsigned long refault;
- bool workingset;
+
int memcgid;
- long nr;
+ struct pglist_data *pgdat;
+ unsigned long eviction;
- if (lru_gen_enabled()) {
- lru_gen_refault(folio, shadow);
- return;
- }
+ if (lru_gen_enabled())
+ return lru_gen_test_recent(shadow, file, workingset);
- unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
+ unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset);
eviction <<= bucket_order;
- rcu_read_lock();
/*
* Look up the memcg associated with the stored ID. It might
* have been deleted since the folio's eviction.
@@ -425,7 +448,8 @@ void workingset_refault(struct folio *folio, void *shadow)
*/
eviction_memcg = mem_cgroup_from_id(memcgid);
if (!mem_cgroup_disabled() && !eviction_memcg)
- goto out;
+ return false;
+
eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
refault = atomic_long_read(&eviction_lruvec->nonresident_age);
@@ -447,21 +471,6 @@ void workingset_refault(struct folio *folio, void *shadow)
*/
refault_distance = (refault - eviction) & EVICTION_MASK;
- /*
- * The activation decision for this folio is made at the level
- * where the eviction occurred, as that is where the LRU order
- * during folio reclaim is being determined.
- *
- * However, the cgroup that will own the folio is the one that
- * is actually experiencing the refault event.
- */
- nr = folio_nr_pages(folio);
- memcg = folio_memcg(folio);
- pgdat = folio_pgdat(folio);
- lruvec = mem_cgroup_lruvec(memcg, pgdat);
-
- mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
-
mem_cgroup_flush_stats_delayed();
/*
* Compare the distance to the existing workingset size. We
@@ -483,8 +492,51 @@ void workingset_refault(struct folio *folio, void *shadow)
NR_INACTIVE_ANON);
}
}
- if (refault_distance > workingset_size)
+
+ return refault_distance <= workingset_size;
+}
+
+/**
+ * workingset_refault - Evaluate the refault of a previously evicted folio.
+ * @folio: The freshly allocated replacement folio.
+ * @shadow: Shadow entry of the evicted folio.
+ *
+ * Calculates and evaluates the refault distance of the previously
+ * evicted folio in the context of the node and the memcg whose memory
+ * pressure caused the eviction.
+ */
+void workingset_refault(struct folio *folio, void *shadow)
+{
+ bool file = folio_is_file_lru(folio);
+ struct pglist_data *pgdat;
+ struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
+ bool workingset;
+ long nr;
+
+ if (lru_gen_enabled()) {
+ lru_gen_refault(folio, shadow);
+ return;
+ }
+
+ rcu_read_lock();
+
+ nr = folio_nr_pages(folio);
+ memcg = folio_memcg(folio);
+ pgdat = folio_pgdat(folio);
+ lruvec = mem_cgroup_lruvec(memcg, pgdat);
+
+ if (!workingset_test_recent(shadow, file, &workingset)) {
+ /*
+ * The activation decision for this folio is made at the level
+ * where the eviction occurred, as that is where the LRU order
+ * during folio reclaim is being determined.
+ *
+ * However, the cgroup that will own the folio is the one that
+ * is actually experiencing the refault event.
+ */
goto out;
+ }
folio_set_active(folio);
workingset_age_nonresident(lruvec, nr);
@@ -498,6 +550,7 @@ void workingset_refault(struct folio *folio, void *shadow)
mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
}
out:
+ mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
rcu_read_unlock();
}
--
2.30.2
On Thu, Dec 08, 2022 at 12:28:07PM -0800, Nhat Pham wrote:
> + struct address_space *mapping = f.file->f_mapping;
> + pgoff_t first_index = off >> PAGE_SHIFT;
> + pgoff_t last_index =
> + len == 0 ? ULONG_MAX : (off + len - 1) >> PAGE_SHIFT;
> + XA_STATE(xas, &mapping->i_pages, first_index);
> + struct folio *folio;
> +
> + rcu_read_lock();
> + xas_for_each(&xas, folio, last_index) {
> + if (xas_retry(&xas, folio) || !folio)
> + continue;
!folio can't be true. xas_for_each() terminates when folio is NULL.
> + if (xa_is_value(folio)) {
> + /* page is evicted */
> + void *shadow = (void *)folio;
> + bool workingset; /* not used */
> +
> + cs.nr_evicted += 1;
> +
> +#ifdef CONFIG_SWAP /* implies CONFIG_MMU */
> + if (shmem_mapping(mapping)) {
> + /* shmem file - in swap cache */
> + swp_entry_t swp = radix_to_swp_entry(folio);
> +
> + shadow = get_shadow_from_swap_cache(swp);
> + }
> +#endif
> + if (workingset_test_recent(shadow, true, &workingset))
> + cs.nr_recently_evicted += 1;
> +
> + continue;
> + }
> +
> + /* page is in cache */
> + cs.nr_cache += 1;
> +
> + if (folio_test_dirty(folio))
> + cs.nr_dirty += 1;
> +
> + if (folio_test_writeback(folio))
> + cs.nr_writeback += 1;
A folio may represent more than one page. That's the point of folios.
So there should be something in here which does
unsigned long nr = folio_nr_pages();
and then all these '1' should be 'nr'.
Except that you may need to adjust nr if 'first_index' > folio->index, or
'last_index' < folio->index + nr.
You should test this with XFS, AFS or erofs to be sure you're getting
results that look right.
On Mon, Dec 12, 2022 at 7:48 AM Matthew Wilcox <[email protected]> wrote:
>
> On Thu, Dec 08, 2022 at 12:28:07PM -0800, Nhat Pham wrote:
> > + struct address_space *mapping = f.file->f_mapping;
> > + pgoff_t first_index = off >> PAGE_SHIFT;
> > + pgoff_t last_index =
> > + len == 0 ? ULONG_MAX : (off + len - 1) >> PAGE_SHIFT;
> > + XA_STATE(xas, &mapping->i_pages, first_index);
> > + struct folio *folio;
> > +
> > + rcu_read_lock();
> > + xas_for_each(&xas, folio, last_index) {
> > + if (xas_retry(&xas, folio) || !folio)
> > + continue;
>
> !folio can't be true. xas_for_each() terminates when folio is NULL.
Good to know - I'll remove this in the next version.
>
> > + if (xa_is_value(folio)) {
> > + /* page is evicted */
> > + void *shadow = (void *)folio;
> > + bool workingset; /* not used */
> > +
> > + cs.nr_evicted += 1;
> > +
> > +#ifdef CONFIG_SWAP /* implies CONFIG_MMU */
> > + if (shmem_mapping(mapping)) {
> > + /* shmem file - in swap cache */
> > + swp_entry_t swp = radix_to_swp_entry(folio);
> > +
> > + shadow = get_shadow_from_swap_cache(swp);
> > + }
> > +#endif
> > + if (workingset_test_recent(shadow, true, &workingset))
> > + cs.nr_recently_evicted += 1;
> > +
> > + continue;
> > + }
> > +
> > + /* page is in cache */
> > + cs.nr_cache += 1;
> > +
> > + if (folio_test_dirty(folio))
> > + cs.nr_dirty += 1;
> > +
> > + if (folio_test_writeback(folio))
> > + cs.nr_writeback += 1;
>
> A folio may represent more than one page. That's the point of folios.
> So there should be something in here which does
>
> unsigned long nr = folio_nr_pages();
>
> and then all these '1' should be 'nr'.
Yikes, that's a bug that I missed! Thanks for pointing it out.
> Except that you may need to adjust nr if 'first_index' > folio->index, or
> 'last_index' < folio->index + nr.
Sounds good!
>
> You should test this with XFS, AFS or erofs to be sure you're getting
> results that look right.
>
On Thu, Dec 8, 2022 at 9:42 PM Nhat Pham <[email protected]> wrote:
> Implement a new syscall that queries cache state of a file and
> summarizes the number of cached pages, number of dirty pages, number of
> pages marked for writeback, number of (recently) evicted pages, etc. in
> a given range.
>
> NAME
> cachestat - query the page cache status of a file.
>
> SYNOPSIS
> #include <sys/mman.h>
>
> struct cachestat {
> __u64 nr_cache;
> __u64 nr_dirty;
> __u64 nr_writeback;
> __u64 nr_evicted;
> __u64 nr_recently_evicted;
> };
>
> int cachestat(unsigned int fd, off_t off, size_t len,
> size_t cstat_size, struct cachestat *cstat,
> unsigned int flags);
>
> DESCRIPTION
> cachestat() queries the number of cached pages, number of dirty
> pages, number of pages marked for writeback, number of (recently)
> evicted pages, in the bytes range given by `off` and `len`.
>
> These values are returned in a cachestat struct, whose address is
> given by the `cstat` argument.
>
> The `off` and `len` arguments must be non-negative integers. If
> `len` > 0, the queried range is [`off`, `off` + `len`]. If `len` ==
> 0, we will query in the range from `off` to the end of the file.
>
> `cstat_size` allows users to obtain partial results. The syscall
> will copy the first `csstat_size` bytes to the specified userspace
> memory. `cstat_size` must be a non-negative value that is no larger
> than the current size of the cachestat struct.
>
> The `flags` argument is unused for now, but is included for future
> extensibility. User should pass 0 (i.e no flag specified).
>
> RETURN VALUE
> On success, cachestat returns 0. On error, -1 is returned, and errno
> is set to indicate the error.
>
> ERRORS
> EFAULT cstat points to an invalid address.
>
> EINVAL invalid `cstat_size` or `flags`
>
> EBADF invalid file descriptor.
>
> Signed-off-by: Nhat Pham <[email protected]>
> arch/m68k/kernel/syscalls/syscall.tbl | 1 +
Acked-by: Geert Uytterhoeven <[email protected]> [m68k]
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds