From: Michal Hocko <[email protected]>
Subject: memcg: oom: fix totalpages calculation for memory.swappiness==0
oom_badness() takes a totalpages argument which says how many pages are
available and it uses it as a base for the score calculation. The value
is calculated by mem_cgroup_get_limit which considers both limit and
total_swap_pages (resp. memsw portion of it).
This is usually correct but since fe35004f ("mm: avoid swapping out with
swappiness==0") we do not swap when swappiness is 0 which means that we
cannot really use up all the totalpages pages. This in turn confuses oom
score calculation if the memcg limit is much smaller than the available
swap because the used memory (capped by the limit) is negligible comparing
to totalpages so the resulting score is too small if adj!=0 (typically
task with CAP_SYS_ADMIN or non zero oom_score_adj). A wrong process might
be selected as result.
The problem can be worked around by checking mem_cgroup_swappiness==0 and
not considering swap at all in such a case.
Signed-off-by: Michal Hocko <[email protected]>
Acked-by: David Rientjes <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Acked-by: KOSAKI Motohiro <[email protected]>
Acked-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
Documentation/cgroups/memory.txt | 4 ++++
mm/memcontrol.c | 21 +++++++++++++++------
2 files changed, 19 insertions(+), 6 deletions(-)
diff -puN
Documentation/cgroups/memory.txt~memcg-oom-fix-totalpages-calculation-for-memoryswappiness==0
Documentation/cgroups/memory.txt
---
a/Documentation/cgroups/memory.txt~memcg-oom-fix-totalpages-calculation-for-memoryswappiness==0
+++ a/Documentation/cgroups/memory.txt
@@ -466,6 +466,10 @@ Note:
5.3 swappiness
Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
+Please note that unlike the global swappiness, memcg knob set to 0
+really prevents from any swapping even if there is a swap storage
+available. This might lead to memcg OOM killer if there are no file
+pages to reclaim.
Following cgroups' swappiness can't be changed.
- root cgroup (uses /proc/sys/vm/swappiness).
diff -puN
mm/memcontrol.c~memcg-oom-fix-totalpages-calculation-for-memoryswappiness==0
mm/memcontrol.c
---
a/mm/memcontrol.c~memcg-oom-fix-totalpages-calculation-for-memoryswappiness==0
+++ a/mm/memcontrol.c
@@ -1452,17 +1452,26 @@ static int mem_cgroup_count_children(str
static u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
{
u64 limit;
- u64 memsw;
limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
- limit += total_swap_pages << PAGE_SHIFT;
- memsw = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
/*
- * If memsw is finite and limits the amount of swap space available
- * to this memcg, return that limit.
+ * Do not consider swap space if we cannot swap due to swappiness
*/
- return min(limit, memsw);
+ if (mem_cgroup_swappiness(memcg)) {
+ u64 memsw;
+
+ limit += total_swap_pages << PAGE_SHIFT;
+ memsw = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
+
+ /*
+ * If memsw is finite and limits the amount of swap space
+ * available to this memcg, return that limit.
+ */
+ limit = min(limit, memsw);
+ }
+
+ return limit;
}
void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
_
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