linux-kernel - Re: [PATCH 2/2] cgroup: Skip subtree root in cgroup_update_dfl

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Message-ID: <20220728144426.GA26631@blackbody.suse.cz>
Date:   Thu, 28 Jul 2022 16:44:26 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] cgroup: Skip subtree root in
 cgroup_update_dfl_csses()

On Wed, Jul 27, 2022 at 08:58:15PM -0400, Waiman Long <longman@...hat.com> wrote:
> The cgroup_update_dfl_csses() function updates css associations when a
> cgroup's subtree_control file is modified. Any changes made to a cgroup's
> subtree_control file, however, will only affect its descendants but not
> the cgroup itself. 

I find this correct.

> So there is no point in migrating csses associated with that cgroup.
> We can skip them instead.

Alone it's not such a big win but it componds with the recent Tejun's
threadgroup_rwsem elision.

> ---
>  kernel/cgroup/cgroup.c | 9 +++++++++
>  1 file changed, 9 insertions(+)

Feel free to have
Reviewed-by: Michal Koutný <mkoutny@...e.com>