Hi,
Last year at LSF/MM Matthew promptly created the new structure for MM
documentation, but there still was no patches with content.
I've started to work on it a while ago and I wanted to send it out in a
more complete form, but I've got distracted and didn't have time to work
on this.
With fast changes around struct page and the threat of Lorenzo's book,
I've decided to send out what I have till now with a hope that we can
really make this a collaborative effort with people filling paragraph
here and there.
If somebody does not feel like sending formal patches, just send me the
"raw" text my way and I'll deal with the rest.
The text is relatively heavily formatted because I believe the target
audience will prefer html version.
v4:
* squash commits into one (Bagas)
* fix references formatting (kbuild)
* add Reviewed-by and Acked-by tags
v3: https://lore.kernel.org/all/[email protected]
* rephrase ZONE_DMA(32) and ZONE_MOVABLE description (Michal)
* add cross-reference to DMA API
v2: https://lore.kernel.org/all/[email protected]
* rephrase the paragraph inroducing zones (Lorenzo)
* update formatting (Bagas)
* add section stubs (Bagas)
* small fixes here and there
v1: https://lore.kernel.org/all/[email protected]
Mike Rapoport (IBM) (1):
docs/mm: Physical Memory: add structure, introduction and nodes
description
Documentation/core-api/dma-api.rst | 2 +
Documentation/mm/page_reclaim.rst | 2 +
Documentation/mm/physical_memory.rst | 346 +++++++++++++++++++++++++++
3 files changed, 350 insertions(+)
--
2.35.1
From: "Mike Rapoport (IBM)" <[email protected]>
Add structure, introduction and Nodes section to Physical Memory
chapter.
As the new documentation references core-api/dma-api and mm/page_reclaim,
add page labels to those documents.
Reviewed-by: Bagas Sanjaya <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Signed-off-by: Mike Rapoport (IBM) <[email protected]>
---
Documentation/core-api/dma-api.rst | 2 +
Documentation/mm/page_reclaim.rst | 2 +
Documentation/mm/physical_memory.rst | 346 +++++++++++++++++++++++++++
3 files changed, 350 insertions(+)
diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
index 829f20a193ca..c847a5b0a0d3 100644
--- a/Documentation/core-api/dma-api.rst
+++ b/Documentation/core-api/dma-api.rst
@@ -1,3 +1,5 @@
+.. _dma_api:
+
============================================
Dynamic DMA mapping using the generic device
============================================
diff --git a/Documentation/mm/page_reclaim.rst b/Documentation/mm/page_reclaim.rst
index 50a30b7f8ac3..3fccde066436 100644
--- a/Documentation/mm/page_reclaim.rst
+++ b/Documentation/mm/page_reclaim.rst
@@ -1,5 +1,7 @@
.. SPDX-License-Identifier: GPL-2.0
+.. _page_reclaim:
+
============
Page Reclaim
============
diff --git a/Documentation/mm/physical_memory.rst b/Documentation/mm/physical_memory.rst
index 2ab7b8c1c863..3e97794d123b 100644
--- a/Documentation/mm/physical_memory.rst
+++ b/Documentation/mm/physical_memory.rst
@@ -3,3 +3,349 @@
===============
Physical Memory
===============
+
+Linux is available for a wide range of architectures so there is a need for an
+architecture-independent abstraction to represent the physical memory. This
+chapter describes the structures used to manage physical memory in a running
+system.
+
+The first principal concept prevalent in the memory management is
+`Non-Uniform Memory Access (NUMA)
+<https://en.wikipedia.org/wiki/Non-uniform_memory_access>`_.
+With multi-core and multi-socket machines, memory may be arranged into banks
+that incur a different cost to access depending on the “distance” from the
+processor. For example, there might be a bank of memory assigned to each CPU or
+a bank of memory very suitable for DMA near peripheral devices.
+
+Each bank is called a node and the concept is represented under Linux by a
+``struct pglist_data`` even if the architecture is UMA. This structure is
+always referenced to by it's typedef ``pg_data_t``. ``A pg_data_t`` structure
+for a particular node can be referenced by ``NODE_DATA(nid)`` macro where
+``nid`` is the ID of that node.
+
+For NUMA architectures, the node structures are allocated by the architecture
+specific code early during boot. Usually, these structures are allocated
+locally on the memory bank they represent. For UMA architectures, only one
+static ``pg_data_t`` structure called ``contig_page_data`` is used. Nodes will
+be discussed further in Section :ref:`Nodes <nodes>`
+
+The entire physical address space is partitioned into one or more blocks
+called zones which represent ranges within memory. These ranges are usually
+determined by architectural constraints for accessing the physical memory.
+The memory range within a node that corresponds to a particular zone is
+described by a ``struct zone``, typedeffed to ``zone_t``. Each zone has
+one of the types described below.
+
+* ``ZONE_DMA`` and ``ZONE_DMA32`` historically represented memory suitable for
+ DMA by peripheral devices that cannot access all of the addressable
+ memory. For many years there are better more and robust interfaces to get
+ memory with DMA specific requirements (:ref:`DMA API <dma_api>`), but
+ ``ZONE_DMA`` and ``ZONE_DMA32`` still represent memory ranges that have
+ restrictions on how they can be accessed.
+ Depending on the architecture, either of these zone types or even they both
+ can be disabled at build time using ``CONFIG_ZONE_DMA`` and
+ ``CONFIG_ZONE_DMA32`` configuration options. Some 64-bit platforms may need
+ both zones as they support peripherals with different DMA addressing
+ limitations.
+
+* ``ZONE_NORMAL`` is for normal memory that can be accessed by the kernel all
+ the time. DMA operations can be performed on pages in this zone if the DMA
+ devices support transfers to all addressable memory. ``ZONE_NORMAL`` is
+ always enabled.
+
+* ``ZONE_HIGHMEM`` is the part of the physical memory that is not covered by a
+ permanent mapping in the kernel page tables. The memory in this zone is only
+ accessible to the kernel using temporary mappings. This zone is available
+ only on some 32-bit architectures and is enabled with ``CONFIG_HIGHMEM``.
+
+* ``ZONE_MOVABLE`` is for normal accessible memory, just like ``ZONE_NORMAL``.
+ The difference is that the contents of most pages in ``ZONE_MOVABLE`` is
+ movable. That means that while virtual addresses of these pages do not
+ change, their content may move between different physical pages. Often
+ ``ZONE_MOVABLE`` is populated during memory hotplug, but it may be
+ also populated on boot using one of ``kernelcore``, ``movablecore`` and
+ ``movable_node`` kernel command line parameters. See :ref:`Page migration
+ <page_migration>` and :ref:`Memory Hot(Un)Plug <admin_guide_memory_hotplug>`
+ for additional details.
+
+* ``ZONE_DEVICE`` represents memory residing on devices such as PMEM and GPU.
+ It has different characteristics than RAM zone types and it exists to provide
+ :ref:`struct page <Pages>` and memory map services for device driver
+ identified physical address ranges. ``ZONE_DEVICE`` is enabled with
+ configuration option ``CONFIG_ZONE_DEVICE``.
+
+It is important to note that many kernel operations can only take place using
+``ZONE_NORMAL`` so it is the most performance critical zone. Zones are
+discussed further in Section :ref:`Zones <zones>`.
+
+The relation between node and zone extents is determined by the physical memory
+map reported by the firmware, architectural constraints for memory addressing
+and certain parameters in the kernel command line.
+
+For example, with 32-bit kernel on an x86 UMA machine with 2 Gbytes of RAM the
+entire memory will be on node 0 and there will be three zones: ``ZONE_DMA``,
+``ZONE_NORMAL`` and ``ZONE_HIGHMEM``::
+
+ 0 2G
+ +-------------------------------------------------------------+
+ | node 0 |
+ +-------------------------------------------------------------+
+
+ 0 16M 896M 2G
+ +----------+-----------------------+--------------------------+
+ | ZONE_DMA | ZONE_NORMAL | ZONE_HIGHMEM |
+ +----------+-----------------------+--------------------------+
+
+
+With a kernel built with ``ZONE_DMA`` disabled and ``ZONE_DMA32`` enabled and
+booted with ``movablecore=80%`` parameter on an arm64 machine with 16 Gbytes of
+RAM equally split between two nodes, there will be ``ZONE_DMA32``,
+``ZONE_NORMAL`` and ``ZONE_MOVABLE`` on node 0, and ``ZONE_NORMAL`` and
+``ZONE_MOVABLE`` on node 1::
+
+
+ 1G 9G 17G
+ +--------------------------------+ +--------------------------+
+ | node 0 | | node 1 |
+ +--------------------------------+ +--------------------------+
+
+ 1G 4G 4200M 9G 9320M 17G
+ +---------+----------+-----------+ +------------+-------------+
+ | DMA32 | NORMAL | MOVABLE | | NORMAL | MOVABLE |
+ +---------+----------+-----------+ +------------+-------------+
+
+.. _nodes:
+
+Nodes
+=====
+
+As we have mentioned, each node in memory is described by a ``pg_data_t`` which
+is a typedef for a ``struct pglist_data``. When allocating a page, by default
+Linux uses a node-local allocation policy to allocate memory from the node
+closest to the running CPU. As processes tend to run on the same CPU, it is
+likely the memory from the current node will be used. The allocation policy can
+be controlled by users as described in
+Documentation/admin-guide/mm/numa_memory_policy.rst.
+
+Most NUMA architectures maintain an array of pointers to the node
+structures. The actual structures are allocated early during boot when
+architecture specific code parses the physical memory map reported by the
+firmware. The bulk of the node initialization happens slightly later in the
+boot process by free_area_init() function, described later in Section
+:ref:`Initialization <initialization>`.
+
+
+Along with the node structures, kernel maintains an array of ``nodemask_t``
+bitmasks called ``node_states``. Each bitmask in this array represents a set of
+nodes with particular properties as defined by ``enum node_states``:
+
+``N_POSSIBLE``
+ The node could become online at some point.
+``N_ONLINE``
+ The node is online.
+``N_NORMAL_MEMORY``
+ The node has regular memory.
+``N_HIGH_MEMORY``
+ The node has regular or high memory. When ``CONFIG_HIGHMEM`` is disabled
+ aliased to ``N_NORMAL_MEMORY``.
+``N_MEMORY``
+ The node has memory(regular, high, movable)
+``N_CPU``
+ The node has one or more CPUs
+
+For each node that has a property described above, the bit corresponding to the
+node ID in the ``node_states[<property>]`` bitmask is set.
+
+For example, for node 2 with normal memory and CPUs, bit 2 will be set in ::
+
+ node_states[N_POSSIBLE]
+ node_states[N_ONLINE]
+ node_states[N_NORMAL_MEMORY]
+ node_states[N_MEMORY]
+ node_states[N_CPU]
+
+For various operations possible with nodemasks please refer to
+``include/linux/nodemask.h``.
+
+Among other things, nodemasks are used to provide macros for node traversal,
+namely ``for_each_node()`` and ``for_each_online_node()``.
+
+For instance, to call a function foo() for each online node::
+
+ for_each_online_node(nid) {
+ pg_data_t *pgdat = NODE_DATA(nid);
+
+ foo(pgdat);
+ }
+
+Node structure
+--------------
+
+The nodes structure ``struct pglist_data`` is declared in
+``include/linux/mmzone.h``. Here we briefly describe fields of this
+structure:
+
+General
+~~~~~~~
+
+``node_zones``
+ The zones for this node. Not all of the zones may be populated, but it is
+ the full list. It is referenced by this node's node_zonelists as well as
+ other node's node_zonelists.
+
+``node_zonelists``
+ The list of all zones in all nodes. This list defines the order of zones
+ that allocations are preferred from. The ``node_zonelists`` is set up by
+ ``build_zonelists()`` in ``mm/page_alloc.c`` during the initialization of
+ core memory management structures.
+
+``nr_zones``
+ Number of populated zones in this node.
+
+``node_mem_map``
+ For UMA systems that use FLATMEM memory model the 0's node
+ ``node_mem_map`` is array of struct pages representing each physical frame.
+
+``node_page_ext``
+ For UMA systems that use FLATMEM memory model the 0's node
+ ``node_page_ext`` is array of extensions of struct pages. Available only
+ in the kernels built with ``CONFIG_PAGE_EXTENTION`` enabled.
+
+``node_start_pfn``
+ The page frame number of the starting page frame in this node.
+
+``node_present_pages``
+ Total number of physical pages present in this node.
+
+``node_spanned_pages``
+ Total size of physical page range, including holes.
+
+``node_size_lock``
+ A lock that protects the fields defining the node extents. Only defined when
+ at least one of ``CONFIG_MEMORY_HOTPLUG`` or
+ ``CONFIG_DEFERRED_STRUCT_PAGE_INIT`` configuration options are enabled.
+ ``pgdat_resize_lock()`` and ``pgdat_resize_unlock()`` are provided to
+ manipulate ``node_size_lock`` without checking for ``CONFIG_MEMORY_HOTPLUG``
+ or ``CONFIG_DEFERRED_STRUCT_PAGE_INIT``.
+
+``node_id``
+ The Node ID (NID) of the node, starts at 0.
+
+``totalreserve_pages``
+ This is a per-node reserve of pages that are not available to userspace
+ allocations.
+
+``first_deferred_pfn``
+ If memory initialization on large machines is deferred then this is the first
+ PFN that needs to be initialized. Defined only when
+ ``CONFIG_DEFERRED_STRUCT_PAGE_INIT`` is enabled
+
+``deferred_split_queue``
+ Per-node queue of huge pages that their split was deferred. Defined only when ``CONFIG_TRANSPARENT_HUGEPAGE`` is enabled.
+
+``__lruvec``
+ Per-node lruvec holding LRU lists and related parameters. Used only when
+ memory cgroups are disabled. It should not be accessed directly, use
+ ``mem_cgroup_lruvec()`` to look up lruvecs instead.
+
+Reclaim control
+~~~~~~~~~~~~~~~
+
+See also :ref:`Page Reclaim <page_reclaim>`.
+
+``kswapd``
+ Per-node instance of kswapd kernel thread.
+
+``kswapd_wait``, ``pfmemalloc_wait``, ``reclaim_wait``
+ Workqueues used to synchronize memory reclaim tasks
+
+``nr_writeback_throttled``
+ Number of tasks that are throttled waiting on dirty pages to clean.
+
+``nr_reclaim_start``
+ Number of pages written while reclaim is throttled waiting for writeback.
+
+``kswapd_order``
+ Controls the order kswapd tries to reclaim
+
+``kswapd_highest_zoneidx``
+ The highest zone index to be reclaimed by kswapd
+
+``kswapd_failures``
+ Number of runs kswapd was unable to reclaim any pages
+
+``min_unmapped_pages``
+ Minimal number of unmapped file backed pages that cannot be reclaimed.
+ Determined by ``vm.min_unmapped_ratio`` sysctl. Only defined when
+ ``CONFIG_NUMA`` is enabled.
+
+``min_slab_pages``
+ Minimal number of SLAB pages that cannot be reclaimed. Determined by
+ ``vm.min_slab_ratio sysctl``. Only defined when ``CONFIG_NUMA`` is enabled
+
+``flags``
+ Flags controlling reclaim behavior.
+
+Compaction control
+~~~~~~~~~~~~~~~~~~
+
+``kcompactd_max_order``
+ Page order that kcompactd should try to achieve.
+
+``kcompactd_highest_zoneidx``
+ The highest zone index to be compacted by kcompactd.
+
+``kcompactd_wait``
+ Workqueue used to synchronize memory compaction tasks.
+
+``kcompactd``
+ Per-node instance of kcompactd kernel thread.
+
+``proactive_compact_trigger``
+ Determines if proactive compaction is enabled. Controlled by
+ ``vm.compaction_proactiveness`` sysctl.
+
+Statistics
+~~~~~~~~~~
+
+``per_cpu_nodestats``
+ Per-CPU VM statistics for the node
+
+``vm_stat``
+ VM statistics for the node.
+
+.. _zones:
+
+Zones
+=====
+
+.. admonition:: Stub
+
+ This section is incomplete. Please list and describe the appropriate fields.
+
+.. _pages:
+
+Pages
+=====
+
+.. admonition:: Stub
+
+ This section is incomplete. Please list and describe the appropriate fields.
+
+.. _folios:
+
+Folios
+======
+
+.. admonition:: Stub
+
+ This section is incomplete. Please list and describe the appropriate fields.
+
+.. _initialization:
+
+Initialization
+==============
+
+.. admonition:: Stub
+
+ This section is incomplete. Please list and describe the appropriate fields.
--
2.35.1
Gentle ping.
On Sun, Jan 15, 2023 at 08:42:11PM +0200, Mike Rapoport wrote:
> Hi,
>
> Last year at LSF/MM Matthew promptly created the new structure for MM
> documentation, but there still was no patches with content.
>
> I've started to work on it a while ago and I wanted to send it out in a
> more complete form, but I've got distracted and didn't have time to work
> on this.
>
> With fast changes around struct page and the threat of Lorenzo's book,
> I've decided to send out what I have till now with a hope that we can
> really make this a collaborative effort with people filling paragraph
> here and there.
>
> If somebody does not feel like sending formal patches, just send me the
> "raw" text my way and I'll deal with the rest.
>
> The text is relatively heavily formatted because I believe the target
> audience will prefer html version.
>
> v4:
> * squash commits into one (Bagas)
> * fix references formatting (kbuild)
> * add Reviewed-by and Acked-by tags
>
> v3: https://lore.kernel.org/all/[email protected]
> * rephrase ZONE_DMA(32) and ZONE_MOVABLE description (Michal)
> * add cross-reference to DMA API
>
> v2: https://lore.kernel.org/all/[email protected]
> * rephrase the paragraph inroducing zones (Lorenzo)
> * update formatting (Bagas)
> * add section stubs (Bagas)
> * small fixes here and there
>
> v1: https://lore.kernel.org/all/[email protected]
>
> Mike Rapoport (IBM) (1):
> docs/mm: Physical Memory: add structure, introduction and nodes
> description
>
> Documentation/core-api/dma-api.rst | 2 +
> Documentation/mm/page_reclaim.rst | 2 +
> Documentation/mm/physical_memory.rst | 346 +++++++++++++++++++++++++++
> 3 files changed, 350 insertions(+)
>
> --
> 2.35.1
>
--
Sincerely yours,
Mike.
Mike Rapoport <[email protected]> writes:
> Gentle ping.
Is that your way of saying that you think it's perhaps ready to be
applied? I've been watching the discussion but wasn't sure if things
have settled or not.
Thanks,
jon
On Sun, Jan 22, 2023 at 10:43:06AM -0700, Jonathan Corbet wrote:
> Mike Rapoport <[email protected]> writes:
>
> > Gentle ping.
>
> Is that your way of saying that you think it's perhaps ready to be
> applied? I've been watching the discussion but wasn't sure if things
> have settled or not.
Well, everybody who participated in the discussion acked the patch, so
yeah, I think it's ready ;-)
> Thanks,
>
> jon
On 1/15/23 19:42, Mike Rapoport wrote:
> From: "Mike Rapoport (IBM)" <[email protected]>
>
> Add structure, introduction and Nodes section to Physical Memory
> chapter.
>
> As the new documentation references core-api/dma-api and mm/page_reclaim,
> add page labels to those documents.
>
> Reviewed-by: Bagas Sanjaya <[email protected]>
> Reviewed-by: Lorenzo Stoakes <[email protected]>
> Acked-by: Michal Hocko <[email protected]>
> Signed-off-by: Mike Rapoport (IBM) <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
A small bug to fix below?
<snip>
> +
> +Along with the node structures, kernel maintains an array of ``nodemask_t``
> +bitmasks called ``node_states``. Each bitmask in this array represents a set of
> +nodes with particular properties as defined by ``enum node_states``:
> +
> +``N_POSSIBLE``
> + The node could become online at some point.
> +``N_ONLINE``
> + The node is online.
> +``N_NORMAL_MEMORY``
> + The node has regular memory.
> +``N_HIGH_MEMORY``
> + The node has regular or high memory. When ``CONFIG_HIGHMEM`` is disabled
> + aliased to ``N_NORMAL_MEMORY``.
Noted.
> +``N_MEMORY``
> + The node has memory(regular, high, movable)
> +``N_CPU``
> + The node has one or more CPUs
> +
> +For each node that has a property described above, the bit corresponding to the
> +node ID in the ``node_states[<property>]`` bitmask is set.
> +
> +For example, for node 2 with normal memory and CPUs, bit 2 will be set in ::
> +
> + node_states[N_POSSIBLE]
> + node_states[N_ONLINE]
> + node_states[N_NORMAL_MEMORY]
> + node_states[N_MEMORY]
> + node_states[N_CPU]
Should it be set also in node_states[N_HIGH_MEMORY]?
On Tue, Jan 24, 2023 at 12:00:07PM +0100, Vlastimil Babka wrote:
> On 1/15/23 19:42, Mike Rapoport wrote:
> > From: "Mike Rapoport (IBM)" <[email protected]>
> >
> > Add structure, introduction and Nodes section to Physical Memory
> > chapter.
> >
> > As the new documentation references core-api/dma-api and mm/page_reclaim,
> > add page labels to those documents.
> >
> > Reviewed-by: Bagas Sanjaya <[email protected]>
> > Reviewed-by: Lorenzo Stoakes <[email protected]>
> > Acked-by: Michal Hocko <[email protected]>
> > Signed-off-by: Mike Rapoport (IBM) <[email protected]>
>
> Acked-by: Vlastimil Babka <[email protected]>
>
> A small bug to fix below?
>
> <snip>
>
> > +
> > +Along with the node structures, kernel maintains an array of ``nodemask_t``
> > +bitmasks called ``node_states``. Each bitmask in this array represents a set of
> > +nodes with particular properties as defined by ``enum node_states``:
> > +
> > +``N_POSSIBLE``
> > + The node could become online at some point.
> > +``N_ONLINE``
> > + The node is online.
> > +``N_NORMAL_MEMORY``
> > + The node has regular memory.
> > +``N_HIGH_MEMORY``
> > + The node has regular or high memory. When ``CONFIG_HIGHMEM`` is disabled
> > + aliased to ``N_NORMAL_MEMORY``.
>
> Noted.
>
> > +``N_MEMORY``
> > + The node has memory(regular, high, movable)
> > +``N_CPU``
> > + The node has one or more CPUs
> > +
> > +For each node that has a property described above, the bit corresponding to the
> > +node ID in the ``node_states[<property>]`` bitmask is set.
> > +
> > +For example, for node 2 with normal memory and CPUs, bit 2 will be set in ::
> > +
> > + node_states[N_POSSIBLE]
> > + node_states[N_ONLINE]
> > + node_states[N_NORMAL_MEMORY]
> > + node_states[N_MEMORY]
> > + node_states[N_CPU]
>
> Should it be set also in node_states[N_HIGH_MEMORY]?
You mean because of the aliasing of N_NORMAL_MEMORY and N_HIGH_MEMORY?
On January 24, 2023 12:16:20 PM GMT+01:00, Mike Rapoport <[email protected]> wrote:
>On Tue, Jan 24, 2023 at 12:00:07PM +0100, Vlastimil Babka wrote:
>> On 1/15/23 19:42, Mike Rapoport wrote:
>> > From: "Mike Rapoport (IBM)" <[email protected]>
>> >
>> > Add structure, introduction and Nodes section to Physical Memory
>> > chapter.
>> >
>> > As the new documentation references core-api/dma-api and mm/page_reclaim,
>> > add page labels to those documents.
>> >
>> > Reviewed-by: Bagas Sanjaya <[email protected]>
>> > Reviewed-by: Lorenzo Stoakes <[email protected]>
>> > Acked-by: Michal Hocko <[email protected]>
>> > Signed-off-by: Mike Rapoport (IBM) <[email protected]>
>>
>> Acked-by: Vlastimil Babka <[email protected]>
>>
>> A small bug to fix below?
>>
>> <snip>
>>
>> > +
>> > +Along with the node structures, kernel maintains an array of ``nodemask_t``
>> > +bitmasks called ``node_states``. Each bitmask in this array represents a set of
>> > +nodes with particular properties as defined by ``enum node_states``:
>> > +
>> > +``N_POSSIBLE``
>> > + The node could become online at some point.
>> > +``N_ONLINE``
>> > + The node is online.
>> > +``N_NORMAL_MEMORY``
>> > + The node has regular memory.
>> > +``N_HIGH_MEMORY``
>> > + The node has regular or high memory. When ``CONFIG_HIGHMEM`` is disabled
>> > + aliased to ``N_NORMAL_MEMORY``.
>>
>> Noted.
>>
>> > +``N_MEMORY``
>> > + The node has memory(regular, high, movable)
>> > +``N_CPU``
>> > + The node has one or more CPUs
>> > +
>> > +For each node that has a property described above, the bit corresponding to the
>> > +node ID in the ``node_states[<property>]`` bitmask is set.
>> > +
>> > +For example, for node 2 with normal memory and CPUs, bit 2 will be set in ::
>> > +
>> > + node_states[N_POSSIBLE]
>> > + node_states[N_ONLINE]
>> > + node_states[N_NORMAL_MEMORY]
>> > + node_states[N_MEMORY]
>> > + node_states[N_CPU]
>>
>> Should it be set also in node_states[N_HIGH_MEMORY]?
>
>You mean because of the aliasing of N_NORMAL_MEMORY and N_HIGH_MEMORY?
No I meant due to "The node has regular or high memory." Or do I misunderstand?
On Tue, Jan 24, 2023 at 02:40:54PM +0100, Vlastimil Babka wrote:
>
>
> On January 24, 2023 12:16:20 PM GMT+01:00, Mike Rapoport <[email protected]> wrote:
> >On Tue, Jan 24, 2023 at 12:00:07PM +0100, Vlastimil Babka wrote:
> >> On 1/15/23 19:42, Mike Rapoport wrote:
> >> > From: "Mike Rapoport (IBM)" <[email protected]>
> >> >
> >> > Add structure, introduction and Nodes section to Physical Memory
> >> > chapter.
> >> >
> >> > As the new documentation references core-api/dma-api and mm/page_reclaim,
> >> > add page labels to those documents.
> >> >
> >> > Reviewed-by: Bagas Sanjaya <[email protected]>
> >> > Reviewed-by: Lorenzo Stoakes <[email protected]>
> >> > Acked-by: Michal Hocko <[email protected]>
> >> > Signed-off-by: Mike Rapoport (IBM) <[email protected]>
> >>
> >> Acked-by: Vlastimil Babka <[email protected]>
> >>
> >> A small bug to fix below?
> >>
> >> <snip>
> >>
> >> > +
> >> > +Along with the node structures, kernel maintains an array of ``nodemask_t``
> >> > +bitmasks called ``node_states``. Each bitmask in this array represents a set of
> >> > +nodes with particular properties as defined by ``enum node_states``:
> >> > +
> >> > +``N_POSSIBLE``
> >> > + The node could become online at some point.
> >> > +``N_ONLINE``
> >> > + The node is online.
> >> > +``N_NORMAL_MEMORY``
> >> > + The node has regular memory.
> >> > +``N_HIGH_MEMORY``
> >> > + The node has regular or high memory. When ``CONFIG_HIGHMEM`` is disabled
> >> > + aliased to ``N_NORMAL_MEMORY``.
> >>
> >> Noted.
> >>
> >> > +``N_MEMORY``
> >> > + The node has memory(regular, high, movable)
> >> > +``N_CPU``
> >> > + The node has one or more CPUs
> >> > +
> >> > +For each node that has a property described above, the bit corresponding to the
> >> > +node ID in the ``node_states[<property>]`` bitmask is set.
> >> > +
> >> > +For example, for node 2 with normal memory and CPUs, bit 2 will be set in ::
> >> > +
> >> > + node_states[N_POSSIBLE]
> >> > + node_states[N_ONLINE]
> >> > + node_states[N_NORMAL_MEMORY]
> >> > + node_states[N_MEMORY]
> >> > + node_states[N_CPU]
> >>
> >> Should it be set also in node_states[N_HIGH_MEMORY]?
> >
> >You mean because of the aliasing of N_NORMAL_MEMORY and N_HIGH_MEMORY?
>
> No I meant due to "The node has regular or high memory." Or do I misunderstand?
I checked the code, node_states[N_HIGH_MEMORY] will be set indeed.
Will send v5 soon.