Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 28 Jul 2022 16:44:26 +0200
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     Waiman Long <longman@redhat.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] cgroup: Skip subtree root in
 cgroup_update_dfl_csses()
Message-ID: <20220728144426.GA26631@blackbody.suse.cz>
References: <20220728005815.1715522-1-longman@redhat.com>
 <20220728005815.1715522-2-longman@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20220728005815.1715522-2-longman@redhat.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

On Wed, Jul 27, 2022 at 08:58:15PM -0400, Waiman Long <longman@redhat.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 Koutn? <mkoutny@suse.com>