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From:   Waiman Long <llong@redhat.com>
Subject: Re: [PATCH v3 0/9] cgroup/cpuset: Add new cpuset partition type &
 empty effecitve cpus
To:     Tejun Heo <tj@kernel.org>, Waiman Long <llong@redhat.com>
Cc:     Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <shuah@kernel.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kselftest@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>, Phil Auld <pauld@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>
References: <20210720141834.10624-1-longman@redhat.com>
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Message-ID: <1df2d0be-f2b7-3e57-e656-2bcdf2a3c821@redhat.com>
Date:   Mon, 9 Aug 2021 21:12:18 -0400
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On 8/9/21 6:46 PM, Tejun Heo wrote:
> Hello, Waiman. Sorry about the delay. Was off for a while.
>
> On Tue, Jul 27, 2021 at 05:14:27PM -0400, Waiman Long wrote:
>> However, if we have a complicated partition setup with multiple child
>> partitions. Invalid cpuset.cpus change in a parent partition will cause all
>> the child partitions to become invalid too. That is the scenario that I
>> don't want to happen inadvertently. Alternatively, we can restrict those
> I don't think there's anything fundamentally wrong with it given the
> requirement that userland has to monitor invalid state transitions.
> The same mass transition can happen through cpu hotplug operations,
> right?
>
>> invalid changes if a child partition exist and let it pass through and make
>> it invalid if it is a standalone partition.
>>
>> Please let me know which approach do you want me to take.
> I think it'd be best if we can stick to some principles rather than
> trying to adjust it for specific scenarios. e.g.:
>
> * If a given state can be reached through cpu hot [un]plug, any
>    configuration attempt which reaches the same state should be allowed
>    with the same end result as cpu hot [un]plug.
>
> * If a given state can't ever be reached in whichever way, the
>    configuration attempting to reach such state should be rejected.

OK, I got it. I will make the necessary changes and submit a new patch 
series.

Thanks,
Longman