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Date:   Tue, 17 Aug 2021 12:14:08 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Leon Yang <lnyng@fb.com>, Chris Down <chris@chrisdown.name>,
        Roman Gushchin <guro@fb.com>, 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
Message-Id: <20210817121408.47be5d9a11baf5bba44da9a1@linux-foundation.org>
In-Reply-To: <20210817180506.220056-1-hannes@cmpxchg.org>
References: <20210817180506.220056-1-hannes@cmpxchg.org>
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On Tue, 17 Aug 2021 14:05:06 -0400 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
> 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.

Which kernel version(s) do you think need this?