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SubjectRe: [PATCH v2 08/10] cpuset: allow to keep tasks in empty cpusets
Hello, Li.

On Wed, Jun 05, 2013 at 05:16:59PM +0800, Li Zefan wrote:
> @@ -2092,11 +2183,13 @@ static void cpuset_propagate_hotplug_workfn(struct work_struct *work)
> mutex_unlock(&cpuset_mutex);
>
> /*
> - * If @cs became empty, move tasks to the nearest ancestor with
> - * execution resources. This is full cgroup operation which will
> + * If sane_behavior flag is set, we'll keep tasks in empty cpusets.
> + *
> + * Otherwise move tasks to the nearest ancestor with execution
> + * resources. This is full cgroup operation which will
> * also call back into cpuset. Should be done outside any lock.
> */
> - if (is_empty)
> + if (!sane && is_empty)
> remove_tasks_in_empty_cpuset(cs);
>
> /* the following may free @cs, should be the last operation */
> @@ -2171,6 +2264,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
> cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
> mutex_unlock(&callback_mutex);
> /* we don't mess with cpumasks of tasks in top_cpuset */
> + update_tasks_cpumask_hier(&top_cpuset, false, NULL);
> }

I'm a little confused by the order of operation. We now have two
different hierarchical walks for hotplug propagation, right? I
suppose the above one is added because we now also need to update the
mask when cpus are being brought online?

I wonder whether it'd be possible to merge the two paths. My
suspicion is that we probably don't need propagate_hotplug_work
anymore now that we can drop RCU read lock while doing the pre-order
walk. What do you think?

Thanks.

--
tejun


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