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cgroup: implement cgroup_has_tasks() and unexport cgroup_task_count()

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cgroup_task_count() read-locks css_set_lock and walks all tasks to
count them and then returns the result.  The only thing all the users
want is determining whether the cgroup is empty or not.  This patch
implements cgroup_has_tasks() which tests whether cgroup->cset_links
is empty, replaces all cgroup_task_count() usages and unexports it.

Note that the test isn't synchronized.  This is the same as before.
The test has always been racy.

This will help planned css_set locking update.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
This commit is contained in:
Tejun Heo
2014-02-13 06:58:39 -05:00
parent afeb0f9fd4
commit 07bc356ed2
4 changed files with 10 additions and 6 deletions
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4
mm/memcontrol.c
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@@ -4958,7 +4958,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
struct cgroup *cgrp = memcg->css.cgroup;
/* returns EBUSY if there is a task or if we come here twice. */
if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
if (cgroup_has_tasks(cgrp) || !list_empty(&cgrp->children))
return -EBUSY;
/* we call try-to-free pages for make this cgroup empty */
@@ -5140,7 +5140,7 @@ static int __memcg_activate_kmem(struct mem_cgroup *memcg,
* of course permitted.
*/
mutex_lock(&memcg_create_mutex);
if (cgroup_task_count(memcg->css.cgroup) || memcg_has_children(memcg))
if (cgroup_has_tasks(memcg->css.cgroup) || memcg_has_children(memcg))
err = -EBUSY;
mutex_unlock(&memcg_create_mutex);
if (err)