Commit e7b1e851 authored by Barry Song's avatar Barry Song Committed by Kefeng Wang
Browse files

mm: add docs for per-order mTHP counters and transhuge_page ABI 

next inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I9Q9DF
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=42248b9d34ea1be1b959d343fff465906cb787fc

--------------------------------

This patch includes documentation for mTHP counters and an ABI file for
sys-kernel-mm-transparent-hugepage, which appears to have been missing for
some time.

[v-songbaohua@oppo.com: fix the name and unexpected indentation]
  Link: https://lkml.kernel.org/r/20240415054538.17071-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20240412114858.407208-4-21cnbao@gmail.com


Signed-off-by: default avatarBarry Song <v-songbaohua@oppo.com>
Reviewed-by: default avatarRyan Roberts <ryan.roberts@arm.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent e7cfecd5

Documentation/ABI/testing/sysfs-kernel-mm-transparent-hugepage

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What:		/sys/kernel/mm/transparent_hugepage/

Date:		April 2024

Contact:	Linux memory management mailing list <linux-mm@kvack.org>

Description:

		/sys/kernel/mm/transparent_hugepage/ contains a number of files and

		subdirectories,



			- defrag

			- enabled

			- hpage_pmd_size

			- khugepaged

			- shmem_enabled

			- use_zero_page

			- subdirectories of the form hugepages-<size>kB, where <size>

			  is the page size of the hugepages supported by the kernel/CPU

			  combination.



		See Documentation/admin-guide/mm/transhuge.rst for details.

Documentation/admin-guide/mm/transhuge.rst

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@@ -474,6 +474,34 @@ thp_swpout_fallback 
	Usually because failed to allocate some continuous swap space

	for the huge page.



In /sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/stats, There are

also individual counters for each huge page size, which can be utilized to

monitor the system's effectiveness in providing huge pages for usage. Each

counter has its own corresponding file.



anon_fault_alloc

	is incremented every time a huge page is successfully

	allocated and charged to handle a page fault.



anon_fault_fallback

	is incremented if a page fault fails to allocate or charge

	a huge page and instead falls back to using huge pages with

	lower orders or small pages.



anon_fault_fallback_charge

	is incremented if a page fault fails to charge a huge page and

	instead falls back to using huge pages with lower orders or

	small pages even though the allocation was successful.



anon_swpout

	is incremented every time a huge page is swapped out in one

	piece without splitting.



anon_swpout_fallback

	is incremented if a huge page has to be split before swapout.

	Usually because failed to allocate some continuous swap space

	for the huge page.



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