https://github.com/torvalds/linux
Revision c350a99ea2b1b666c28948d74ab46c16913c28a7 authored by Roman Gushchin on 25 August 2019, 00:54:47 UTC, committed by Linus Torvalds on 25 August 2019, 02:48:42 UTC
Percpu caching of local vmstats with the conditional propagation by the cgroup tree leads to an accumulation of errors on non-leaf levels. Let's imagine two nested memory cgroups A and A/B. Say, a process belonging to A/B allocates 100 pagecache pages on the CPU 0. The percpu cache will spill 3 times, so that 32*3=96 pages will be accounted to A/B and A atomic vmstat counters, 4 pages will remain in the percpu cache. Imagine A/B is nearby memory.max, so that every following allocation triggers a direct reclaim on the local CPU. Say, each such attempt will free 16 pages on a new cpu. That means every percpu cache will have -16 pages, except the first one, which will have 4 - 16 = -12. A/B and A atomic counters will not be touched at all. Now a user removes A/B. All percpu caches are freed and corresponding vmstat numbers are forgotten. A has 96 pages more than expected. As memory cgroups are created and destroyed, errors do accumulate. Even 1-2 pages differences can accumulate into large numbers. To fix this issue let's accumulate and propagate percpu vmstat values before releasing the memory cgroup. At this point these numbers are stable and cannot be changed. Since on cpu hotplug we do flush percpu vmstats anyway, we can iterate only over online cpus. Link: http://lkml.kernel.org/r/20190819202338.363363-2-guro@fb.com Fixes: 42a300353577 ("mm: memcontrol: fix recursive statistics correctness & scalabilty") Signed-off-by: Roman Gushchin <guro@fb.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Tip revision: c350a99ea2b1b666c28948d74ab46c16913c28a7 authored by Roman Gushchin on 25 August 2019, 00:54:47 UTC
mm: memcontrol: flush percpu vmstats before releasing memcg
mm: memcontrol: flush percpu vmstats before releasing memcg
Tip revision: c350a99
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lib | ||
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net | ||
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.cocciconfig | -rw-r--r-- | 59 bytes |
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Makefile | -rw-r--r-- | 59.7 KB |
README | -rw-r--r-- | 727 bytes |
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