Messages in this thread | | | Date | Tue, 28 Apr 2020 17:16:51 -0400 | From | Johannes Weiner <> | Subject | Re: [PATCH 1/2] mm, memcg: Avoid stale protection values when cgroup is above protection |
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On Tue, Apr 28, 2020 at 07:26:47PM +0100, Chris Down wrote: > From: Yafang Shao <laoar.shao@gmail.com> > > A cgroup can have both memory protection and a memory limit to isolate > it from its siblings in both directions - for example, to prevent it > from being shrunk below 2G under high pressure from outside, but also > from growing beyond 4G under low pressure. > > Commit 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim") > implemented proportional scan pressure so that multiple siblings in > excess of their protection settings don't get reclaimed equally but > instead in accordance to their unprotected portion. > > During limit reclaim, this proportionality shouldn't apply of course: > there is no competition, all pressure is from within the cgroup and > should be applied as such. Reclaim should operate at full efficiency. > > However, mem_cgroup_protected() never expected anybody to look at the > effective protection values when it indicated that the cgroup is above > its protection. As a result, a query during limit reclaim may return > stale protection values that were calculated by a previous reclaim cycle > in which the cgroup did have siblings. > > When this happens, reclaim is unnecessarily hesitant and potentially > slow to meet the desired limit. In theory this could lead to premature > OOM kills, although it's not obvious this has occurred in practice. > > Fixes: 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim") > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > Signed-off-by: Chris Down <chris@chrisdown.name> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Michal Hocko <mhocko@kernel.org> > Cc: Roman Gushchin <guro@fb.com> > > [hannes@cmpxchg.org: rework code comment] > [hannes@cmpxchg.org: changelog] > [chris@chrisdown.name: fix store tear] > [chris@chrisdown.name: retitle]
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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