[lkml]   [2019]   [Aug]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 1/2] mm: memcontrol: flush percpu vmstats before releasing memcg
On Mon, 12 Aug 2019 15:29:10 -0700 Roman Gushchin <> wrote:

> 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.
> Fixes: 42a300353577 ("mm: memcontrol: fix recursive statistics correctness & scalabilty")

Is this not serious enough for a cc:stable?

 \ /
  Last update: 2019-08-13 23:29    [W:0.058 / U:0.296 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site