linux-kernel - Re: [PATCH-cgroup] cgroup/cpuset: Enable invalid to valid local partition transition

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Date:   Mon, 2 Oct 2023 13:40:51 -0400
From:   Waiman Long <longman@...hat.com>
To:     Pierre Gondois <pierre.gondois@....com>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH-cgroup] cgroup/cpuset: Enable invalid to valid local
 partition transition

On 10/2/23 06:06, Pierre Gondois wrote:
> Hello Waiman,
>
> I could test the patch using the for-next branch in your tree.
> Just a NIT, it seemed that the message indicating the reason
> the isolated configuration was invalid is not printed anymore:
>
> Commands:
> # mkdir cgroup
> # mount -t cgroup2 none cgroup/
> # mkdir cgroup/A1 cgroup/B1
> # echo "+cpuset" > cgroup/cgroup.subtree_control
> # echo 0-3 > cgroup/A1/cpuset.cpus
> # echo isolated > cgroup/A1/cpuset.cpus.partition
> # echo 4-6 > cgroup/B1/cpuset.cpus
> # cat cgroup/A1/cpuset.cpus.partition
> isolated
> # echo 0-4 > cgroup/A1/cpuset.cpus
> # cat cgroup/A1/cpuset.cpus.partition
> isolated invalid                      <--- used to have '(Cpu list in 
> cpuset.cpus not exclusive)'
> # echo 0-3 > cgroup/A1/cpuset.cpus
> # cat cgroup/A1/cpuset.cpus.partition
> isolated                              <--- now working!
>
>
> But when creating an isolated partition from overlapping cpusets,
> the message is printed:
> # mkdir cgroup
> # mount -t cgroup2 none cgroup/
> # mkdir cgroup/A1 cgroup/B1
> # echo "+cpuset" > cgroup/cgroup.subtree_control
> # echo 0-4 > cgroup/A1/cpuset.cpus
> # echo 4-6 > cgroup/B1/cpuset.cpus
> # echo isolated > cgroup/B1/cpuset.cpus.partition
>
> # cat cgroup/A1/cpuset.cpus.partition
> member
> # cat cgroup/B1/cpuset.cpus.partition
> isolated invalid (Cpu list in cpuset.cpus not exclusive) <--- Complete 
> message printed
>
>
> On 9/30/23 05:44, Waiman Long wrote:
>> When a local partition becomes invalid, it won't transition back to
>> valid partition automatically if a proper "cpuset.cpus.exclusive" or
>> "cpuset.cpus" change is made. Instead, system administrators have to
>> explicitly echo "root" or "isolated" into the "cpuset.cpus.partition"
>> file at the partition root.
>>
>> This patch now enables the automatic transition of an invalid local
>> partition back to valid when there is a proper "cpuset.cpus.exclusive"
>> or "cpuset.cpus" change.
>>
>> Automatic transition of an invalid remote partition to a valid one,
>> however, is not covered by this patch. They still need an explicit
>> write to "cpuset.cpus.partition" to become valid again.
>
> I'm not sure I understand what is meant by 'remote partition',
> is it possible to explain ? Or is the following illustrating what you
> mean ?
>
> # mkdir cgroup
> # mount -t cgroup2 none cgroup/
> # mkdir cgroup/A1 cgroup/B1
> # echo "+cpuset" > cgroup/cgroup.subtree_control
> # echo 0-3 > cgroup/A1/cpuset.cpus
> # echo isolated > cgroup/A1/cpuset.cpus.partition
> # echo 4-6 > cgroup/B1/cpuset.cpus
> # echo isolated > cgroup/B1/cpuset.cpus.partition
>
> # echo 0-4 > cgroup/A1/cpuset.cpus
> # cat cgroup/A1/cpuset.cpus.partition
> isolated invalid
> # cat cgroup/B1/cpuset.cpus.partition
> isolated invalid
>
> # echo 0-3 > cgroup/A1/cpuset.cpus
> # cat cgroup/A1/cpuset.cpus.partition
> isolated
> # cat cgroup/B1/cpuset.cpus.partition
> isolated invalid        <--- The remote CPU is not updated

It is probably another corner case that has not been handled. I will 
look into that.

Thanks for the test.

-Longman