Re: [PATCH v10 5/9] cpuset: Make sure that domain roots work properly with CPU hotplug

[Peter Zijlstra]

On Mon, Jun 18, 2018 at 12:14:04PM +0800, Waiman Long wrote:
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 5ee5e77..6ef3516 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1626,6 +1626,13 @@ Cpuset Interface Files
>  	2) No CPU that has been distributed to child scheduling domain
>  	   roots is deleted.
>  
> +	When all the CPUs allocated to a scheduling domain are offlined,
> +	that scheduling domain will be temporaily gone and all the
> +	tasks in that scheduling domain will migrate to another one that
> +	belongs to the parent of the scheduling domain root.  When any
> +	of those offlined CPUs is onlined again, a new scheduling domain
> +	will be re-created and the tasks will be migrated back.
> +

You should mention that this is a destructive operation. If any of the
tasks had an affinity smaller than the original cgroup, that will be
gone.