linux-kernel - Re: [PATCH] mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim

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Message-ID: <YRwRzjOexeXbkirV@carbon.dhcp.thefacebook.com>
Date:   Tue, 17 Aug 2021 12:45:18 -0700
From:   Roman Gushchin <guro@...com>
To:     Johannes Weiner <hannes@...xchg.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Leon Yang <lnyng@...com>, Chris Down <chris@...isdown.name>,
        Michal Hocko <mhocko@...e.com>, <linux-mm@...ck.org>,
        <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel-team@...com>
Subject: Re: [PATCH] mm: memcontrol: fix occasional OOMs due to proportional
 memory.low reclaim

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@...com>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

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

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

?


Thanks!