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From: Roman Gushchin <>
To: Rik van Riel <>
Cc: Andrew Morton <>, <>,
	<>, <>,
	<>, Michal Hocko <>,
	Chris Down <>,
	Johannes Weiner <>
Subject: Re: [PATCH] mm,vmscan: fix divide by zero in get_scan_count
Date: Fri, 27 Aug 2021 09:28:12 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, Aug 26, 2021 at 10:01:49PM -0400, Rik van Riel wrote:
> Changeset f56ce412a59d ("mm: memcontrol: fix occasional OOMs due to
> proportional memory.low reclaim") introduced a divide by zero corner
> case when oomd is being used in combination with cgroup memory.low
> protection.
> When oomd decides to kill a cgroup, it will force the cgroup memory
> to be reclaimed after killing the tasks, by writing to the memory.max
> file for that cgroup, forcing the remaining page cache and reclaimable
> slab to be reclaimed down to zero.
> Previously, on cgroups with some memory.low protection that would result
> in the memory being reclaimed down to the memory.low limit, or likely not
> at all, having the page cache reclaimed asynchronously later.
> With f56ce412a59d the oomd write to memory.max tries to reclaim all the
> way down to zero, which may race with another reclaimer, to the point of
> ending up with the divide by zero below.
> This patch implements the obvious fix.
> Fixes: f56ce412a59d ("mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim")
> Signed-off-by: Rik van Riel <>

It looks like we discover a new divide-by-zero corner case after every
functional change to the memory protection code :)

Acked-by: Roman Gushchin <>

Thanks, Rik!

  reply	other threads:[~2021-08-27 16:28 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-27  2:01 [PATCH] mm,vmscan: fix divide by zero in get_scan_count Rik van Riel
2021-08-27 16:28 ` Roman Gushchin [this message]
2021-08-30 11:33 ` Michal Hocko
2021-08-30 13:24   ` Rik van Riel
2021-08-30 13:41     ` Michal Hocko
2021-08-30 20:48 ` Johannes Weiner
2021-08-31  9:59   ` Michal Hocko
2021-08-31 15:48     ` Rik van Riel
2021-09-01 19:40       ` Johannes Weiner
2021-08-31 12:58 ` Chris Down

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