linux-kernel - [PATCH] mm: writeback: ratelimit stat flush from mem_cgroup_wb

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Message-ID: <20240118184235.618164-1-shakeelb@google.com>
Date: Thu, 18 Jan 2024 18:42:35 +0000
From: Shakeel Butt <shakeelb@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, 
	Johannes Weiner <hannes@...xchg.org>, Tejun Heo <tj@...nel.org>
Cc: Jan Kara <jack@...e.cz>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Michal Hocko <mhocko@...nel.org>, Muchun Song <muchun.song@...ux.dev>, cgroups@...r.kernel.org, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Shakeel Butt <shakeelb@...gle.com>
Subject: [PATCH] mm: writeback: ratelimit stat flush from mem_cgroup_wb_stats

One of our workloads (Postgres 14) has regressed when migrated from 5.10
to 6.1 upstream kernel. The regression can be reproduced by sysbench's
oltp_write_only benchmark. It seems like the always on rstat flush in
mem_cgroup_wb_stats() is causing the regression. So, rate limit that
specific rstat flush. One potential consequence would be the dirty
throttling might be decided on stale memcg stats. However from our
benchmarks and production traffic we have not observed any change in the
dirty throttling behavior of the application.

Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 935f48c4d399..2474c8382e6f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4776,7 +4776,7 @@ void mem_cgroup_wb_stats(struct bdi_writeback *wb, unsigned long *pfilepages,
 	struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
 	struct mem_cgroup *parent;
 
-	mem_cgroup_flush_stats(memcg);
+	mem_cgroup_flush_stats_ratelimited(memcg);
 
 	*pdirty = memcg_page_state(memcg, NR_FILE_DIRTY);
 	*pwriteback = memcg_page_state(memcg, NR_WRITEBACK);
-- 
2.43.0.429.g432eaa2c6b-goog