Re: [PATCH v2 2/2] mm: add docs for per-order mTHP split counters
From: Barry Song
Date: Fri Jun 28 2024 - 23:08:45 EST
On Sat, Jun 29, 2024 at 1:09 AM Lance Yang <ioworker0@xxxxxxxxx> wrote:
>
> This commit introduces documentation for mTHP split counters in
> transhuge.rst.
>
> Signed-off-by: Mingzhe Yang <mingzhe.yang@xxxxxx>
> Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
Reviewed-by: Barry Song <baohua@xxxxxxxxxx>
> ---
> 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
>