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
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------------------------------------------------------
From: Michal Koutný <mkoutny@xxxxxxxx>
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@xxxxxxxxxx
Fixes: 230671533d64 ("mm: memory.low hierarchical behavior")
Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.18+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_counter.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/mm/page_counter.c~mm-fix-protection-usage-propagation
+++ a/mm/page_counter.c
@@ -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.
_
Patches currently in -mm which might be from mkoutny@xxxxxxxx are
mm-fix-protection-usage-propagation.patch
proc-pid-smaps-consistent-whitespace-output-format.patch
