cpuset: allow to keep tasks in empty cpusets
To achieve this:
- We call update_tasks_cpumask/nodemask() for empty cpusets when
hotplug happens, instead of moving tasks out of them.
- When a cpuset's masks are changed by writing cpuset.cpus/mems,
we also update tasks in child cpusets which are empty.
v3:
- do propagation work in one place for both hotplug and unplug
v2:
- drop rcu_read_lock before calling update_task_nodemask() and
update_task_cpumask(), instead of using workqueue.
- add documentation in include/linux/cgroup.h
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index d0ad379..53e81a6 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -277,6 +277,10 @@
*
* - Remount is disallowed.
*
+ * - cpuset: tasks will be kept in empty cpusets when hotplug happens
+ * and take masks of ancestors with non-empty cpus/mems, instead of
+ * being moved to an ancestor.
+ *
* - memcg: use_hierarchy is on by default and the cgroup file for
* the flag is not created.
*