Re: [PATCH v4 4/6] cgroup/cpuset: Allow non-top parent partition root to distribute out all CPUs

[Waiman Long]

On 8/11/21 2:13 PM, Tejun Heo wrote:
> On Tue, Aug 10, 2021 at 11:06:05PM -0400, Waiman Long wrote:
> > Currently, a parent partition root cannot distribute all its CPUs to
> > child partition roots with no CPUs left. However in some use cases,
> > a management application may want to create a parent partition root as
> > a management unit with no task associated with it and has all its CPUs
> > distributed to various child partition roots dynamically according to
> > their needs. Leaving a cpu in the parent partition root in such a case is
> > now a waste.
> >
> > To accommodate such use cases, a parent partition root can now have
> > all its CPUs distributed to its child partition roots as long as:
> >   1) it is not the top cpuset; and
> >   2) there is no task directly associated with the parent.
> >
> > Once an empty parent partition root is formed, no new task can be moved
> > into it.
> The above are already enforced by cgroup2 core, right? No intermediate
> cgroup with controllers enabled can have processes. From controllers' POV,
> only leaves can have processes.
I don't think that is true. A task can reside anywhere in the cgroup 
hierarchy. I have encountered no problem moving tasks around.

Cheers,
Longman