Messages in this thread | | | Date | Tue, 31 Aug 2021 13:58:21 +0100 | From | Chris Down <> | Subject | Re: [PATCH] mm,vmscan: fix divide by zero in get_scan_count |
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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 >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 <riel@surriel.com>
Thanks, good catch. No strong preference on this vs. max3(), so feel free to keep my ack either way.
Acked-by: Chris Down <chris@chrisdown.name>
> >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 > >
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