linux-kernel - Re: [PATCH v8 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst

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Message-ID: <583191c1-4153-cee8-1836-a4037b9ea304@redhat.com>
Date:   Fri, 3 Dec 2021 14:27:20 -0500
From:   Waiman Long <longman@...hat.com>
To:     Michal Koutný <mkoutny@...e.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 v8 5/6] cgroup/cpuset: Update description of
 cpuset.cpus.partition in cgroup-v2.rst

On 12/3/21 13:25, Michal Koutný wrote:
> Hello Longman.
>
> On Wed, Dec 01, 2021 at 08:28:09PM -0500, Waiman Long <longman@...hat.com> wrote:
>> 1) The limitation that "cpuset.cpus" has to be a superset of child's
>> "cpuset.cpus" has been removed as a new patch to remove that limitation will
>> be added.
> Superb!
>
>> 2) The initial transition from "member" to partition root now requires that
>> "cpuset.cpus" overlap with that of the parent's "cpuset.cpus" instead of
>> being a superset.
> That's sensible.
>
>> For the transition back to "member", I haven't changed the current wording
>> of forcing child partition roots to become "member" yet. If you think
>> keeping them as invalid partition root is better, I can made that change
>> too.
> I wrote I was indifferent about this in a previous mail but when I think
> about it now, switching to invalid root is perhaps better than switching
> to member since it'd effectively mean that modifications of the parent
> config propagate (permanently) also to a descendant config, which is
> an undesired v1-ism.

That makes sense. I will keep those child partitions in an invalid state 
then.

>
>> Please let me know what other changes you would like to see.
> I hope my remarks below are just clarifications and not substantial
> changes. Besides that I find your new draft good. Thanks!
>
>> [...]
>>      An invalid partition root can be reverted back to a valid one
>>      if none of the validity constraints of a valid partition root
>>      are violated.
> s/can be/will be/
>
> (I understand the intention is to make it asynchronously and
> automatically, i.e. without writing into the affected descendant(s)
> cpuset.partition again.)
Yes, that will be automatic and the partition will become valid again if 
other events cause changes that unbreak the validity constraints.
>
>>      Poll and inotify events are triggered whenever the state of
>>      "cpuset.cpus.partition" changes.  That includes changes caused by
>>      write to "cpuset.cpus.partition", cpu hotplug and other changes
>>      that make the partition invalid.
> -> that change validity status
>
> (In accordance with the comment above.)
Cheers,
Longman