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mm: add docs for per-order mTHP split counters

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This commit introduces documentation for mTHP split counters in
transhuge.rst.

[ioworker0@gmail.com: improve the doc as suggested by Ryan]
  Link: https://lkml.kernel.org/r/20240704012905.42971-3-ioworker0@gmail.com
[ioworker0@gmail.com: tweak Documentation/admin-guide/mm/transhuge.rst]
  Link: https://lkml.kernel.org/r/20240707013659.1151-1-ioworker0@gmail.com
Link: https://lkml.kernel.org/r/20240628130750.73097-3-ioworker0@gmail.com
Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Bang Li <libang.li@antgroup.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lance Yang 2024-06-28 21:07:50 +08:00 committed by Andrew Morton
parent f216c845f3
commit 9b89e01899
1 changed files with 15 additions and 4 deletions
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19
Documentation/admin-guide/mm/transhuge.rst
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@ -369,10 +369,6 @@ also applies to the regions registered in khugepaged.
Monitoring usage
================
.. note::
Currently the below counters only record events relating to
PMD-sized THP. Events relating to other THP sizes are not included.
The number of PMD-sized anonymous transparent huge pages currently used by the
system is available by reading the AnonHugePages field in ``/proc/meminfo``.
To identify what applications are using PMD-sized anonymous transparent huge
@ -514,6 +510,21 @@ file_fallback_charge
falls back to using small pages even though the allocation was
successful.
split
is incremented every time a huge page is successfully split into
smaller orders. This can happen for a variety of reasons but a
common reason is that a huge page is old and is being reclaimed.
split_failed
is incremented if kernel fails to split huge
page. This can happen if the page was pinned by somebody.
split_deferred
is incremented when a huge page is put onto split queue.
This happens when a huge page is partially unmapped and splitting
it would free up some memory. Pages on split queue are going to
be split under memory pressure, if splitting is possible.
As the system ages, allocating huge pages may be expensive as the
system uses memory compaction to copy data around memory to free a
huge page for use. There are some counters in ``/proc/vmstat`` to help