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

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Date: Fri, 26 Jan 2024 13:20:48 -0800
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Johannes Weiner <hannes@...xchg.org>
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 1:06 PM Johannes Weiner <hannes@...xchg.org> wrote:
>
> 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>

Thanks Shakeel and Johannes. v2 is here, hopefully fixed up correctly:
https://lore.kernel.org/all/20240126211927.1171338-1-tjmercier@google.com/