linux-kernel - Re: [PATCH] mm/vmscan: drop checking if _deferred_list is empty before using TTU

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Message-Id: <20240701233235.a1ae705c72ba6f81531c21fd@linux-foundation.org>
Date: Mon, 1 Jul 2024 23:32:35 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Barry Song <21cnbao@...il.com>
Cc: Ryan Roberts <ryan.roberts@....com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>, David
 Hildenbrand <david@...hat.com>
Subject: Re: [PATCH] mm/vmscan: drop checking if _deferred_list is empty
 before using TTU_SYNC

On Mon, 1 Jul 2024 21:35:41 +1200 Barry Song <21cnbao@...il.com> wrote:

> > > +++ b/mm/vmscan.c
> > > @@ -1291,7 +1291,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
> > >                        * try_to_unmap acquire PTL from the first PTE,
> > >                        * eliminating the influence of temporary PTE values.
> > >                        */
> > > -                     if (folio_test_large(folio) && list_empty(&folio->_deferred_list))
> > > +                     if (folio_test_large(folio))
> >
> > As it stands, the list_empty() technically needs a data_race() annotation. I
> > think your original patch went into v6.10-rc1? If so, perhaps it makes sense to
> > try to get this into the next rc?
> 
> Either way is fine. Hi Andrew, if you include it for the next RC, could you
> please add this tag?
> 
> Fixes: 73bc32875ee9 ("mm: hold PTL from the first PTE while reclaiming
> a large folio")

Nope!  That invites people to backport this change into kernels which
don't contain Ryan's 5ed890ce5147 ("mm: vmscan: avoid split during
shrink_folio_list()").

I'll simply queue this in the normal fashion.

> And an additional changelog:
> 
> Additionally, the list_empty() technically requires a data_race() annotation.

Done, thanks.