mm: memcg: don't periodically flush stats when memcg is disabled

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.

Link: https://lkml.kernel.org/r/20240126211927.1171338-1-tjmercier@google.com
Fixes: aa48e47e3906 ("memcg: infrastructure to flush memcg stats")
Signed-off-by: T.J. Mercier <tjmercier@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Chris Li <chrisl@kernel.org>
Reported-by: Minchan Kim <minchan@google.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Michal Koutn <mkoutny@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index df11d6d19ee38f97ee96062207cb5956b9ca2f39..484a9d2862d4fe05a3a1495a6566cd312f725f37 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5621,7 +5621,7 @@ 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);