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

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Date:   Mon, 13 Jun 2022 13:06:20 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     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>,
        Michal Koutný <mkoutny@...e.com>
Subject: Re: [PATCH v11 7/8] cgroup/cpuset: Update description of
 cpuset.cpus.partition in cgroup-v2.rst

On 6/13/22 09:18, Waiman Long wrote:
> On 6/12/22 23:12, Tejun Heo 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.
>
> No, it doesn't affect parent at all. It just limit whats the siblings 
> can do due to their mutual constraint. If this is what the confusion 
> is about, I will try to reword the doc text.

I am planning to make the following change to the documentation patch. 
Please let me know if that can clarify the confusion, if any.

Thanks,
Longman

diff --git a/Documentation/admin-guide/cgroup-v2.rst 
b/Documentation/admin-guid>
index 9184a09e0fc9..9cbfa25dab97 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2176,7 +2175,8 @@ Cpuset Interface Files

         For a valid partition root or an invalid partition root with
         the exclusivity rule enabled, changes made to "cpuset.cpus"
-       that violate the exclusivity rule will not be allowed.
+       that violate the exclusivity rule with its siblings will not
+       be allowed.

         A valid non-root parent partition may distribute out all its CPUs
         to its child partitions when there is no task associated with it.