[PATCH] memcg: collect oom back off statistics

[Michal Hocko]

OOM killer might back off and not kill anything if it believes that the
memcg is not really OOM because there is a task(s) which is on the way
out and so it would free memory shortly.

We however do not have any way data to know how much those heuristics
are effective to prevent from the real killing. Let's add a statistic
for this event so we can collect data and make some educated conclusions
from it.

Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
---
 mm/memcontrol.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f016d26adfd3..b3c839ac6a1d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -100,6 +100,7 @@ enum mem_cgroup_events_index {
 	MEM_CGROUP_EVENTS_PGPGOUT,	/* # of pages paged out */
 	MEM_CGROUP_EVENTS_PGFAULT,	/* # of page-faults */
 	MEM_CGROUP_EVENTS_PGMAJFAULT,	/* # of major page-faults */
+	MEM_CGROUP_EVENTS_OOM_BACK_OFF,	/* # of oom killer backoffs */
 	MEM_CGROUP_EVENTS_NSTATS,
 };
 
@@ -108,6 +109,7 @@ static const char * const mem_cgroup_events_names[] = {
 	"pgpgout",
 	"pgfault",
 	"pgmajfault",
+	"oom_back_off",
 };
 
 static const char * const mem_cgroup_lru_names[] = {
@@ -1752,6 +1754,13 @@ static u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
 	return limit;
 }
 
+static void mem_cgroup_inc_oom_backoff(struct mem_cgroup *memcg)
+{
+	preempt_disable();
+	this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_OOM_BACK_OFF]);
+	preempt_enable();
+}
+
 static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 				     int order)
 {
@@ -1768,6 +1777,7 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	 */
 	if (fatal_signal_pending(current) || current->flags & PF_EXITING) {
 		set_thread_flag(TIF_MEMDIE);
+		mem_cgroup_inc_oom_backoff(memcg);
 		return;
 	}
 
@@ -1795,6 +1805,7 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 				mem_cgroup_iter_break(memcg, iter);
 				if (chosen)
 					put_task_struct(chosen);
+				mem_cgroup_inc_oom_backoff(memcg);
 				return;
 			case OOM_SCAN_OK:
 				break;
-- 
1.8.5.2


-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/