linux-kernel - Re: [PATCH] cgroup: Return if dst_cgrp equals to src

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Message-ID: <Yo6zAi+Y/uXLYUI7@blackbook>
Date:   Thu, 26 May 2022 00:51:46 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     shisiyuan19870131@...il.com
Cc:     Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup: Return if dst_cgrp equals to src_cgrp

Hello.

On Sat, May 21, 2022 at 01:02:00AM +0800, shisiyuan <shisiyuan19870131@...il.com> wrote:
> In function cgroup_migrate_add_src(), if dst_cgrp
> equals to src_cgroup which the tasks link, dont
> go on migrating tasks to another css_set.

Do you have an example which operations lead to this situation?

> This can save the cost of unnecessary migration.

How much are the savings visible?

(Note, I suspect the shortcut on `src_cgrp == dst_cgrp` might not be
always correct when called from cgroup_update_dfl_csses() but not 100%
sure now.)

Thanks,
Michal