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

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Message-ID: <jazycqhefxn6oigmt6mitn2cfoonscbdwqxy5g7gs2j74w3ia5@qwcu3v7kmk4h>
Date: Mon, 22 Jan 2024 16:20:31 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Shakeel Butt <shakeelb@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>, Tejun Heo <tj@...nel.org>, 
	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
Subject: Re: [PATCH] mm: writeback: ratelimit stat flush from
 mem_cgroup_wb_stats

Hello.

On Thu, Jan 18, 2024 at 06:42:35PM +0000, Shakeel Butt <shakeelb@...gle.com> wrote:
> 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.

Is the affected benchmark running in a non-root cgroup?

I'm asking whether this would warrant a 
  Fixes: fd25a9e0e23b ("memcg: unify memcg stat flushing") 
that introduced the global flush (in v6.1) but it was removed later in 
  7d7ef0a4686a ("mm: memcg: restore subtree stats flushing") 
(so v6.8 could be possibly unaffected).

Thanks,
Michal

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