mm/page_counter.c: fix protection usage propagation
commit a6f23d14 upstream. When workload runs in cgroups that aren't directly below root cgroup and their parent specifies reclaim protection, it may end up ineffective. The reason is that propagate_protected_usage() is not called in all hierarchy up. All the protected usage is incorrectly accumulated in the workload's parent. This means that siblings_low_usage is overestimated and effective protection underestimated. Even though it is transitional phenomenon (uncharge path does correct propagation and fixes the wrong children_low_usage), it can undermine the intended protection unexpectedly. We have noticed this problem while seeing a swap out in a descendant of a protected memcg (intermediate node) while the parent was conveniently under its protection limit and the memory pressure was external to that hierarchy. Michal has pinpointed this down to the wrong siblings_low_usage which led to the unwanted reclaim. The fix is simply updating children_low_usage in respective ancestors also in the charging path. Fixes: 23067153 ("mm: memory.low hierarchical behavior") Signed-off-by:Michal Koutný <mkoutny@suse.com> Signed-off-by:
Michal Hocko <mhocko@suse.com> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Acked-by:
Michal Hocko <mhocko@suse.com> Acked-by:
Roman Gushchin <guro@fb.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Tejun Heo <tj@kernel.org> Cc: <stable@vger.kernel.org> [4.18+] Link: http://lkml.kernel.org/r/20200803153231.15477-1-mhocko@kernel.org Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:
Paul Gortmaker <paul.gortmaker@windriver.com>
parent
70d12ec7
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