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mm: add docs for per-order mTHP counters and transhuge_page ABI
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: Barry Song <v-songbaohua@oppo.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: David 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: Andrew Morton <akpm@linux-foundation.org>
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What: /sys/kernel/mm/transparent_hugepage/
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Date: April 2024
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Contact: Linux memory management mailing list <linux-mm@kvack.org>
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Description:
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/sys/kernel/mm/transparent_hugepage/ contains a number of files and
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subdirectories,
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- defrag
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- enabled
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- hpage_pmd_size
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- khugepaged
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- shmem_enabled
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- use_zero_page
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- subdirectories of the form hugepages-<size>kB, where <size>
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is the page size of the hugepages supported by the kernel/CPU
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combination.
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See Documentation/admin-guide/mm/transhuge.rst for details.
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@ -447,6 +447,34 @@ thp_swpout_fallback
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Usually because failed to allocate some continuous swap space
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for the huge page.
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In /sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/stats, There are
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also individual counters for each huge page size, which can be utilized to
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monitor the system's effectiveness in providing huge pages for usage. Each
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counter has its own corresponding file.
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anon_fault_alloc
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is incremented every time a huge page is successfully
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allocated and charged to handle a page fault.
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anon_fault_fallback
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is incremented if a page fault fails to allocate or charge
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a huge page and instead falls back to using huge pages with
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lower orders or small pages.
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anon_fault_fallback_charge
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is incremented if a page fault fails to charge a huge page and
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instead falls back to using huge pages with lower orders or
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small pages even though the allocation was successful.
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anon_swpout
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is incremented every time a huge page is swapped out in one
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piece without splitting.
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anon_swpout_fallback
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is incremented if a huge page has to be split before swapout.
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Usually because failed to allocate some continuous swap space
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for the huge page.
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As the system ages, allocating huge pages may be expensive as the
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system uses memory compaction to copy data around memory to free a
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huge page for use. There are some counters in ``/proc/vmstat`` to help
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