Re: [PATCH 3/5] cgroup/cpuset: Allow non-top parent partition root to distribute out all CPUs

Waiman Long
2021-06-17T20:45:43Z

On 6/16/21 4:57 PM, Tejun Heo wrote:
> Hello,
>
> On Thu, Jun 03, 2021 at 05:24:14PM -0400, Waiman Long wrote:
>> @@ -2181,6 +2192,13 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>> (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed)))
>> goto out_unlock;
>>
>> + /*
>> + * On default hierarchy, task cannot be moved to a cpuset with empty
>> + * effective cpus.
>> + */
>> + if (is_in_v2_mode() && cpumask_empty(cs->effective_cpus))
>> + goto out_unlock;
>> +
> This is inconsistent with how other events which leave a root partition
> empty is handled. Woudln't it be more consistent to switch the parent to
> PRS_ERROR and behave accordingly but allow it to have valid child roots?

From my point of view, PRS_ERROR is used when cpus are gone because of
cpu hotplug (offline). It can be a temporary condition that will be
corrected later on. I don't want to use PRS_ERROR for the particular
case that the users have explicitly distributed out all the cpus to
child partitions. I will clarify it in the next version and double check
to make sure that this rule is consistently apply.

Thanks,
Longman