+ mm-memcg-dont-periodically-flush-stats-when-memcg-is-disabled.patch added to mm-unstable branch

+ mm-memcg-dont-periodically-flush-stats-when-memcg-is-disabled.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: memcg: don't periodically flush stats when memcg is disabled
has been added to the -mm mm-unstable branch.  Its filename is
     mm-memcg-dont-periodically-flush-stats-when-memcg-is-disabled.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-dont-periodically-flush-stats-when-memcg-is-disabled.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "T.J. Mercier" <tjmercier@google.com>
Subject: mm: memcg: don't periodically flush stats when memcg is disabled
Date: Fri, 26 Jan 2024 21:19:25 +0000

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>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/memcontrol.c~mm-memcg-dont-periodically-flush-stats-when-memcg-is-disabled
+++ a/mm/memcontrol.c
@@ -5622,7 +5622,7 @@ static int mem_cgroup_css_online(struct
 	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);
_

Patches currently in -mm which might be from tjmercier@google.com are

mm-memcg-dont-periodically-flush-stats-when-memcg-is-disabled.patch