LKML Archive on
help / color / mirror / Atom feed
From: Chris Down <>
To: Rik van Riel <>
Cc: Andrew Morton <>,,,,,
	Michal Hocko <>,
	Johannes Weiner <>
Subject: Re: [PATCH] mm,vmscan: fix divide by zero in get_scan_count
Date: Tue, 31 Aug 2021 13:58:21 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Rik van Riel writes:
>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
>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 <>

Thanks, good catch. No strong preference on this vs. max3(), so feel free to 
keep my ack either way.

Acked-by: Chris Down <>

>diff --git a/mm/vmscan.c b/mm/vmscan.c
>index eeae2f6bc532..f1782b816c98 100644
>--- a/mm/vmscan.c
>+++ b/mm/vmscan.c
>@@ -2592,7 +2592,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> 			cgroup_size = max(cgroup_size, protection);
> 			scan = lruvec_size - lruvec_size * protection /
>-				cgroup_size;
>+				(cgroup_size + 1);
> 			/*
> 			 * Minimally target SWAP_CLUSTER_MAX pages to keep

      parent reply	other threads:[~2021-08-31 12:58 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
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 [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).