linux-kernel - Re: [PATCH v9 3/7] cgroup/cpuset: Refining features and constraints of a partition

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Date:   Thu, 16 Dec 2021 10:28:37 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, 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 v9 3/7] cgroup/cpuset: Refining features and constraints
 of a partition

On Wed, Dec 15, 2021 at 11:29:41AM -0500, Waiman Long <longman@...hat.com> wrote:
> There are additional checks for the member to partition transition which
> requires that the target cpuset shouldn't have child cpuset.

Ah, I forgot the transition condition no. 4 will apply here. Clear.

So, currently full bottom up + top down walk is needed in (rare?) case
the switch from root partition to member and back.

> That prevents the recovering of a invalid partition root under a
> member cpuset. We could certainly remove that restriction by adding
> additional code as well as additional tests to verify it works. I
> haven't done that simply to avoid adding more complexity to the
> current code.

I agree this restriction can be lifted later independently when the rest
settles.  (It's not so different from controllers disabling on the
unified hierarchy after all.)


Thanks,
Michal