linux-kernel - Re: [PATCH] mm: migrate: drop redundant anonymous statistics for file folios migration

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Message-ID: <CAGsJ_4xZDrCSjv5NA7T_yDyjKbCB8XsADPQxCnq2qRO8gU=VaA@mail.gmail.com>
Date: Thu, 5 Dec 2024 19:33:27 +1300
From: Barry Song <21cnbao@...il.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, david@...hat.com, ying.huang@...ux.alibaba.com, 
	ziy@...dia.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: migrate: drop redundant anonymous statistics for file
 folios migration

On Thu, Dec 5, 2024 at 7:06 PM Baolin Wang
<baolin.wang@...ux.alibaba.com> wrote:
>
>
>
> On 2024/12/5 13:00, Barry Song wrote:
> > On Thu, Dec 5, 2024 at 4:54 PM Baolin Wang
> > <baolin.wang@...ux.alibaba.com> wrote:
> >>
> >> Commit 5d65c8d758f2 ("mm: count the number of anonymous THPs per size") adds
> >> a new anonymous counter per THP size, however, when folio_mapping() is not NULL
> >> during folio migration, it means this is not an anonymous folio, so remove the
> >> redundant anonymous statistics in this case.
> >
> > why? Are you sure anon folios won't call __folio_migrate_mapping()?
> > folio->mapping is PAGE_MAPPING_ANON for anon folios.
> >
> > static __always_inline bool folio_test_anon(const struct folio *folio)
> > {
> >          return ((unsigned long)folio->mapping & PAGE_MAPPING_ANON) != 0;
> > }
>
> Ah, sorry for noise. This just caught my eyes when reading the code, and
> I did not think about it deeply before sending a quick patch. Thanks to
> Barry and Ying for the reminder.

No worries. I recall encountering a negative count during the development of
the original patch and eventually realizing it was due to forgetting
to increment
the migrated anon folios. Your patch seems to reintroduce the bug I encountered
back then :-)

>
> Andrew, please drop this quick patch. Sorry for the trouble.
>

Thanks
Barry