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From: Shakeel Butt <shakeelb@google.com>
Date: Mon, 22 Jan 2024 10:19:10 -0800
Message-ID: <CALvZod4XUrQMxptBo56Fm6-ETQy_DtVq-g4NKokVvSyGwDOnxg@mail.gmail.com>
Subject: Re: [PATCH] mm: writeback: ratelimit stat flush from mem_cgroup_wb_stats
To: =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Jens Axboe <axboe@kernel.dk>, 
	Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>, Jan Kara <jack@suse.cz>, 
	Roman Gushchin <roman.gushchin@linux.dev>, Michal Hocko <mhocko@kernel.org>, 
	Muchun Song <muchun.song@linux.dev>, cgroups@vger.kernel.org, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org
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On Mon, Jan 22, 2024 at 7:20=E2=80=AFAM Michal Koutn=C3=BD <mkoutny@suse.co=
m> wrote:
>
> Hello.
>
> On Thu, Jan 18, 2024 at 06:42:35PM +0000, Shakeel Butt <shakeelb@google.c=
om> wrote:
> > One of our workloads (Postgres 14) has regressed when migrated from 5.1=
0
> > 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).
>

Yes, the benchmark and the workload were running in non-root cgroups.

Regarding the Fixes, please note that the regression was still there
with 7d7ef0a4686a ("mm: memcg: restore subtree stats flushing"), so I
would say that our first conversion to rstat infra would most probably
have the issue as well which was 2d146aa3aa84 ("mm: memcontrol: switch
to rstat").

So, the following fixes tag makes sense to me:

Fixes: 2d146aa3aa84 ("mm: memcontrol: switch to rstat")