linux-kernel - Re: [PATCH v2 2/2] mm: add docs for per-order mTHP split counters

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Date: Sat, 29 Jun 2024 15:08:25 +1200
From: Barry Song <21cnbao@...il.com>
To: Lance Yang <ioworker0@...il.com>
Cc: akpm@...ux-foundation.org, dj456119@...il.com, ryan.roberts@....com, 
	david@...hat.com, shy828301@...il.com, ziy@...dia.com, libang.li@...group.com, 
	baolin.wang@...ux.alibaba.com, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Mingzhe Yang <mingzhe.yang@...com>
Subject: Re: [PATCH v2 2/2] mm: add docs for per-order mTHP split counters

On Sat, Jun 29, 2024 at 1:09 AM Lance Yang <ioworker0@...il.com> wrote:
>
> This commit introduces documentation for mTHP split counters in
> transhuge.rst.
>
> Signed-off-by: Mingzhe Yang <mingzhe.yang@...com>
> Signed-off-by: Lance Yang <ioworker0@...il.com>

Reviewed-by: Barry Song <baohua@...nel.org>

> ---
>  Documentation/admin-guide/mm/transhuge.rst | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index 1f72b00af5d3..709fe10b60f4 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -514,6 +514,22 @@ 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
> +       base pages. This can happen for a variety of reasons but a common
> +       reason is that a huge page is old and is being reclaimed.
> +       This action implies splitting any block mappings into PTEs.
> +
> +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.
> +
>  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
> --
> 2.45.2
>