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 22:30:04 +0800
From: Lance Yang <ioworker0@...il.com>
To: Barry Song <21cnbao@...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

Hi Barry,

Thanks a lot for taking time to review!

On Sat, Jun 29, 2024 at 11:08 AM Barry Song <21cnbao@...il.com> wrote:
>
> 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>

Have a nice weekend ;)
Lance

>
> > ---
> >  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
> >