linux-kernel - Re: [PATCH v11 7/8] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst

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Message-ID: <20220613142452.GB6910@blackbody.suse.cz>
Date:   Mon, 13 Jun 2022 16:24:52 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Waiman Long <longman@...hat.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v11 7/8] cgroup/cpuset: Update description of
 cpuset.cpus.partition in cgroup-v2.rst

On Sun, Jun 12, 2022 at 05:12:51PM -1000, Tejun Heo <tj@...nel.org> wrote:
> Hello,
> 
> On Sun, Jun 12, 2022 at 11:02:38PM -0400, Waiman Long wrote:
> > That is the behavior enforced by setting the CPU_EXCLUSIVE bit in cgroup v1.
> > I haven't explicitly change it to make it different in cgroup v2. The major
> > reason is that I don't want change to one cpuset to affect a sibling
> > partition as it may make the code more complicate to validate if a partition
> > is valid.
> 
> If at all possible, I'd really like to avoid situations where a parent can't
> withdraw resources due to something that a descendant does.

My understanding of the discussed paragraph is that the changes are only
disallowed only among siblings on one level (due to exclusivity rule,
checked in validate_change()). A change in parent won't affect
(non)exclusivity of (valid) children so it's simply allowed.

So the docs (and implementation by a quick look) is sensible.

Michal

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