[PATCH v3 8/8] memcg: do not modify rstat tree for zero updates

From: Yosry Ahmed <yosryahmed@google.com>
To: "Tejun Heo" <tj@kernel.org>, "Josef Bacik" <josef@toxicpanda.com>,
	"Jens Axboe" <axboe@kernel.dk>,
	"Zefan Li" <lizefan.x@bytedance.com>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Michal Hocko" <mhocko@kernel.org>,
	"Roman Gushchin" <roman.gushchin@linux.dev>,
	"Shakeel Butt" <shakeelb@google.com>,
	"Muchun Song" <muchun.song@linux.dev>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Michal Koutný" <mkoutny@suse.com>
Cc: Vasily Averin <vasily.averin@linux.dev>,
	cgroups@vger.kernel.org, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	bpf@vger.kernel.org, Yosry Ahmed <yosryahmed@google.com>,
	Michal Hocko <mhocko@suse.com>
Subject: [PATCH v3 8/8] memcg: do not modify rstat tree for zero updates
Date: Thu, 30 Mar 2023 19:18:01 +0000	[thread overview]
Message-ID: <20230330191801.1967435-9-yosryahmed@google.com> (raw)
In-Reply-To: <20230330191801.1967435-1-yosryahmed@google.com>

In some situations, we may end up calling memcg_rstat_updated() with a
value of 0, which means the stat was not actually updated. An example is
if we fail to reclaim any pages in shrink_folio_list().

Do not add the cgroup to the rstat updated tree in this case, to avoid
unnecessarily flushing it.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 mm/memcontrol.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 361c0bbf7283..a63ee2efa780 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -618,6 +618,9 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
 {
 	unsigned int x;
 
+	if (!val)
+		return;
+
 	cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id());
 
 	x = __this_cpu_add_return(stats_updates, abs(val));
-- 
2.40.0.348.gf938b09366-goog

