linux-kernel - Re: [PATCH cgroup/for-6.20 v4 4/5] cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict

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Message-ID: <f33eb2b3-c2f4-48ae-b2cd-67c0fc0b4877@redhat.com>
Date: Mon, 12 Jan 2026 09:51:28 -0500
From: Waiman Long <llong@...hat.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
 Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
 Sun Shaojie <sunshaojie@...inos.cn>, Chen Ridong
 <chenridong@...weicloud.com>, Chen Ridong <chenridong@...wei.com>
Subject: Re: [PATCH cgroup/for-6.20 v4 4/5] cgroup/cpuset: Don't invalidate
 sibling partitions on cpuset.cpus conflict

On 1/12/26 5:51 AM, Michal Koutný wrote:
> On Sun, Jan 11, 2026 at 11:08:55PM -0500, Waiman Long <longman@...hat.com> wrote:
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> ...
>> @@ -2632,6 +2641,9 @@ Cpuset Interface Files
>>   
>>   	The root cgroup is always a partition root and its state cannot
>>   	be changed.  All other non-root cgroups start out as "member".
>> +	Even though the "cpuset.cpus.exclusive*" control files are not
>> +	present in the root cgroup, they are implicitly the same as
>> +	"cpuset.cpus".
> cpuset.cpus.effective (that one is on root cpuset cg)
>
> (This was likely lost among my v2 comments.)

Sorry, I might have missed this comment of yours. The 
"cpuset.cpus.exclusive" file lists all the CPUs that can be granted to 
its children as exclusive CPUs. The cgroup root is an implicit partition 
root where all its CPUs can be granted to its children whether they are 
online or offline. "cpuset.cpus.effective" OTOH ignores the offline CPUs 
as well as exclusive CPUs that have been passed down to existing 
descendant partition roots so it may differ from the implicit 
"cpuset.cpus.exclusive".

Cheers,
Longman