@@ -72,7 +72,7 @@ void page_counter_charge(struct page_cou
long new;
new = atomic_long_add_return(nr_pages, &c->usage);
- propagate_protected_usage(counter, new);
+ propagate_protected_usage(c, new);
/*
* This is indeed racy, but we can live with some
* inaccuracy in the watermark.
@@ -116,7 +116,7 @@ bool page_counter_try_charge(struct page
new = atomic_long_add_return(nr_pages, &c->usage);
if (new > c->max) {
atomic_long_sub(nr_pages, &c->usage);
- propagate_protected_usage(counter, new);
+ propagate_protected_usage(c, new);
/*
* This is racy, but we can live with some
* inaccuracy in the failcnt.
@@ -125,7 +125,7 @@ bool page_counter_try_charge(struct page
*fail = c;
goto failed;
}
- propagate_protected_usage(counter, new);
+ propagate_protected_usage(c, new);
/*
* Just like with failcnt, we can live with some
* inaccuracy in the watermark.
The patch titled Subject: mm/page_counter.c: fix protection usage propagation has been added to the -mm tree. Its filename is mm-fix-protection-usage-propagation.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-fix-protection-usage-propagation.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-fix-protection-usage-propagation.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Michal Koutný <mkoutny@suse.com> Subject: mm/page_counter.c: fix protection usage propagation 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 indended 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. Link: http://lkml.kernel.org/r/20200803153231.15477-1-mhocko@kernel.org Fixes: 230671533d64 ("mm: memory.low hierarchical behavior") Signed-off-by: Michal Koutný <mkoutny@suse.com> Signed-off-by: Michal Hocko <mhocko@suse.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Roman Gushchin <guro@fb.com> Cc: Tejun Heo <tj@kernel.org> Cc: <stable@vger.kernel.org> [4.18+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- mm/page_counter.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)