[PATCH v2] mm: memcg: Don't periodically flush stats when memcg is disabled

[T.J. Mercier]

The root memcg is onlined even when memcg is disabled. When it's onlined
a 2 second periodic stat flush is started, but no stat flushing is
required when memcg is disabled because there can be no child memcgs.
Most calls to flush memcg stats are avoided when memcg is disabled as a
result of the mem_cgroup_disabled check added in 7d7ef0a4686a
("mm: memcg: restore subtree stats flushing"), but the periodic flushing
started in mem_cgroup_css_online is not. Skip it.

Fixes: aa48e47e3906 ("memcg: infrastructure to flush memcg stats")
Reported-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: T.J. Mercier <tjmercier@xxxxxxxxxx>
Acked-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e4c8735e7c85..bad8f9dfc9ab 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5586,7 +5586,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	if (alloc_shrinker_info(memcg))
 		goto offline_kmem;
 
-	if (unlikely(mem_cgroup_is_root(memcg)))
+	if (unlikely(mem_cgroup_is_root(memcg)) && !mem_cgroup_disabled())
 		queue_delayed_work(system_unbound_wq, &stats_flush_dwork,
 				   FLUSH_TIME);
 	lru_gen_online_memcg(memcg);
-- 
2.43.0.429.g432eaa2c6b-goog