linux-kernel - Re: [PATCH v14 05/12] cpuset: Add an error state to cpuset.sched.partition

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Date:   Tue, 6 Nov 2018 09:17:29 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kernel-team@...com, pjt@...gle.com, luto@...capital.net,
        Mike Galbraith <efault@....de>, torvalds@...ux-foundation.org,
        Roman Gushchin <guro@...com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Tom Hromatka <tom.hromatka@...cle.com>
Subject: Re: [PATCH v14 05/12] cpuset: Add an error state to
 cpuset.sched.partition

On 11/06/2018 06:37 AM, Peter Zijlstra wrote:
> On Mon, Oct 15, 2018 at 04:29:30PM -0400, Waiman Long wrote:
>> Handling error returned by update_parent_subparts_cpumask() in
>> update_cpumasks_hier() is problematic as the states may become
>> inconsistent. To avoid that and increase flexibility in handling other
>> error cases, a new error state (-1) is added to the partition_root_state
>> flag. This new error state is set internally and user cannot write this
>> value to "cpuset.sched.partition".
>>
>> In this error state, the partition root becomes an erroneous one. It is
>> no longer a real partition root, but the CS_CPU_EXCLUSIVE flag will
>> still be set as it can be changed back to a real one if appropriate
>> change happens later on.
> I feel this Changelog should be much more explicit about the reasons
> this -1 state can happen. As is, I've got no clue.

OK, I will elaborate more on this changelog.

Cheers,
Longman