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Date:   Wed, 18 Aug 2021 10:16:59 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Leon Yang <lnyng@fb.com>, Chris Down <chris@chrisdown.name>,
        Roman Gushchin <guro@fb.com>, Michal Hocko <mhocko@suse.com>,
        Linux MM <linux-mm@kvack.org>,
        Cgroups <cgroups@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH] mm: memcontrol: fix occasional OOMs due to proportional
 memory.low reclaim
Message-ID: <YR0WW2VvgtUHK1HL@cmpxchg.org>
References: <20210817180506.220056-1-hannes@cmpxchg.org>
 <CALvZod7097PHnXoOUZzPpmkASKpL3rV+2UJ+zp-NCdkpVoFTWg@mail.gmail.com>
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On Tue, Aug 17, 2021 at 12:10:16PM -0700, Shakeel Butt wrote:
> On Tue, Aug 17, 2021 at 11:03 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
> >
> > We've noticed occasional OOM killing when memory.low settings are in
> > effect for cgroups. This is unexpected and undesirable as memory.low
> > is supposed to express non-OOMing memory priorities between cgroups.
> >
> > The reason for this is proportional memory.low reclaim. When cgroups
> > are below their memory.low threshold, reclaim passes them over in the
> > first round, and then retries if it couldn't find pages anywhere else.
> > But when cgroups are slighly above their memory.low setting, page scan
> 
> *slightly
> 
> > force is scaled down and diminished in proportion to the overage, to
> > the point where it can cause reclaim to fail as well - only in that
> > case we currently don't retry, and instead trigger OOM.
> >
> > To fix this, hook proportional reclaim into the same retry logic we
> > have in place for when cgroups are skipped entirely. This way if
> > reclaim fails and some cgroups were scanned with dimished pressure,
> 
> *diminished

Oops. Andrew, would you mind folding these into the checkpatch fixlet?

> > we'll try another full-force cycle before giving up and OOMing.
> >
> > Reported-by: Leon Yang <lnyng@fb.com>
> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> 
> Should this be considered for stable?

Yes, I think so after all. Please see my reply to Roman.

> Reviewed-by: Shakeel Butt <shakeelb@google.com>

Thanks Shakeel!