From: Rik van Riel riel@surriel.com Subject: mm,vmscan: fix divide by zero in get_scan_count
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.
Link: https://lkml.kernel.org/r/20210826220149.058089c6@imladris.surriel.com Fixes: f56ce412a59d ("mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim") Signed-off-by: Rik van Riel riel@surriel.com Acked-by: Roman Gushchin guro@fb.com Acked-by: Michal Hocko mhocko@suse.com Acked-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Chris Down chris@chrisdown.name Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/vmscan.c~mmvmscan-fix-divide-by-zero-in-get_scan_count +++ a/mm/vmscan.c @@ -2715,7 +2715,7 @@ out: 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 _