From mboxrd@z Thu Jan  1 00:00:00 1970
From: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
Subject: Re: [PATCH] mm: memcontrol: fix occasional OOMs due to proportional
 memory.low reclaim
Date: Wed, 18 Aug 2021 10:16:59 -0400
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To: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Leon Yang <lnyng-b10kYP2dOMg@public.gmane.org>, Chris Down <chris-6Bi1550iOqEnzZ6mRAm98g@public.gmane.org>, Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>, Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>, Linux MM <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Kernel Team <kernel-team-b10kYP2dOMg@public.gmane.org>

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-druUgvl0LCNAfugRpC6u6w@public.gmane.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-b10kYP2dOMg@public.gmane.org>
> > Signed-off-by: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> 
> Should this be considered for stable?

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

> Reviewed-by: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

Thanks Shakeel!