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Date:   Tue, 17 Aug 2021 12:45:18 -0700
From:   Roman Gushchin <guro@fb.com>
To:     Johannes Weiner <hannes@cmpxchg.org>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Leon Yang <lnyng@fb.com>, Chris Down <chris@chrisdown.name>,
        Michal Hocko <mhocko@suse.com>, <linux-mm@kvack.org>,
        <cgroups@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <kernel-team@fb.com>
Subject: Re: [PATCH] mm: memcontrol: fix occasional OOMs due to proportional
 memory.low reclaim
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References: <20210817180506.220056-1-hannes@cmpxchg.org>
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On Tue, Aug 17, 2021 at 02:05:06PM -0400, Johannes Weiner 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
> 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,
> 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>

Acked-by: Roman Gushchin <guro@fb.com>

I guess it's a stable material, so maybe adding:
Fixes: 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim")

?


Thanks!