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SubjectRe: [PATCH v9 2/7] cgroup/cpuset: Allow no-task partition to have empty cpuset.cpus.effective
On Sun, Dec 05, 2021 at 01:32:15PM -0500, Waiman Long wrote:
> adding = deleting = false;
> old_prs = new_prs = cpuset->partition_root_state;
> if (cmd == partcmd_enable) {
> + /*
> + * Enabling partition root is not allowed if not all the CPUs
> + * can be granted from parent's effective_cpus.
> + */
> + if (!cpumask_subset(cpuset->cpus_allowed, parent->effective_cpus))
> + return -EINVAL;
> +
> + /*
> + * A parent can be left with no CPU as long as there is no
> + * task directly associated with the parent partition. For
> + * such a parent, no new task can be moved into it.
> + */
> + if (partition_is_populated(parent, cpuset) &&
> + cpumask_equal(cpuset->cpus_allowed, parent->effective_cpus))
> + return -EINVAL;

So, given that this only happens with threaded domains, can we just not
allow partitions within threaded domains? The combination doesn't make whole
lot of sense to me anyway.

> + /*
> + * 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;

And then we can avoid this extra restriction too, right?

Thanks.

--
tejun

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