linux-kernel - Re: [PATCH] smaps: count large pages smaller than PMD size to anonymous

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Message-ID: <CABzRoyZOJJKWyx4Aj0CQ17Om3wZPixJYMgZ24VSVQ5BRh2EdJw@mail.gmail.com>
Date: Fri, 6 Dec 2024 19:16:10 +0800
From: Lance Yang <ioworker0@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: Wenchao Hao <haowenchao22@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Matthew Wilcox <willy@...radead.org>, Oscar Salvador <osalvador@...e.de>, 
	Muhammad Usama Anjum <usama.anjum@...labora.com>, Andrii Nakryiko <andrii@...nel.org>, 
	Ryan Roberts <ryan.roberts@....com>, Peter Xu <peterx@...hat.com>, Barry Song <21cnbao@...il.com>, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH] smaps: count large pages smaller than PMD size to anonymous_thp

On Tue, Dec 3, 2024 at 10:17 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 03.12.24 14:49, Wenchao Hao wrote:
> > Currently, /proc/xxx/smaps reports the size of anonymous huge pages for
> > each VMA, but it does not include large pages smaller than PMD size.
> >
> > This patch adds the statistics of anonymous huge pages allocated by
> > mTHP which is smaller than PMD size to AnonHugePages field in smaps.
> >
> > Signed-off-by: Wenchao Hao <haowenchao22@...il.com>
> > ---
> >   fs/proc/task_mmu.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 38a5a3e9cba2..b655011627d8 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -717,6 +717,12 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
> >               if (!folio_test_swapbacked(folio) && !dirty &&
> >                   !folio_test_dirty(folio))
> >                       mss->lazyfree += size;
> > +
> > +             /*
> > +              * Count large pages smaller than PMD size to anonymous_thp
> > +              */
> > +             if (!compound && PageHead(page) && folio_order(folio))
> > +                     mss->anonymous_thp += folio_size(folio);
> >       }
> >
> >       if (folio_test_ksm(folio))
>
>
> I think we decided to leave this (and /proc/meminfo) be one of the last
> interfaces where this is only concerned with PMD-sized ones:
>
> Documentation/admin-guide/mm/transhuge.rst:
>
> The number of PMD-sized anonymous transparent huge pages currently used by the
> system is available by reading the AnonHugePages field in ``/proc/meminfo``.
> To identify what applications are using PMD-sized anonymous transparent huge
> pages, it is necessary to read ``/proc/PID/smaps`` and count the AnonHugePages
> fields for each mapping. (Note that AnonHugePages only applies to traditional
> PMD-sized THP for historical reasons and should have been called
> AnonHugePmdMapped).

Yeah, I think we need to keep AnonHugePages unchanged within these interfaces
due to historical reasons ;)

Perhaps, there might be another way to count all THP allocated for each process.

Thanks,
Lance


>
>
>
> --
> Cheers,
>
> David / dhildenb
>
>