linux-kernel - Re: [PATCH] mm: memcg: Don't periodically flush stats when memcg is disabled

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Date: Fri, 26 Jan 2024 16:06:42 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: "T.J. Mercier" <tjmercier@...gle.com>
Cc: Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeelb@...gle.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>, android-mm@...gle.com,
	Minchan Kim <minchan@...gle.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memcg: Don't periodically flush stats when memcg is
 disabled

On Fri, Jan 26, 2024 at 08:33:52PM +0000, T.J. Mercier wrote:
> 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 [1] added in [2], but the
> periodic flushing started in mem_cgroup_css_online is not. Skip it.
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/memcontrol.c?h=v6.8-rc1#n753
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7d7ef0a4686abe43cd76a141b340a348f45ecdf2
> 
> Fixes: aa48e47e3906 ("memcg: infrastructure to flush memcg stats")
> Reported-by: Minchan Kim <minchan@...gle.com>
> Signed-off-by: T.J. Mercier <tjmercier@...gle.com>

With what Shakeel pointed out resolved:

Acked-by: Johannes Weiner <hannes@...xchg.org>