Commit d8423011 authored Oct 26, 2012 by Michal Hocko Committed by Tejun Heo Oct 29, 2012

memcg: root_cgroup cannot reach mem_cgroup_move_parent



The root cgroup cannot be destroyed so we never hit it down the
mem_cgroup_pre_destroy path and mem_cgroup_force_empty_write shouldn't
even try to do anything if called for the root.

This means that mem_cgroup_move_parent doesn't have to bother with the
root cgroup and it can assume it can always move charges upwards.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

parent c26251f9

mm/memcontrol.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -2715,9 +2715,7 @@ static int mem_cgroup_move_parent(struct page *page,
		unsigned long uninitialized_var(flags);
		int ret;

		/* Is ROOT ? */
		if (mem_cgroup_is_root(child))
		return -EINVAL;
		VM_BUG_ON(mem_cgroup_is_root(child));

		ret = -EBUSY;
		if (!get_page_unless_zero(page))
		@@ -3823,6 +3821,8 @@ static int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event)
		struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
		int ret;

		if (mem_cgroup_is_root(memcg))
		return -EINVAL;
		css_get(&memcg->css);
		ret = mem_cgroup_force_empty(memcg);
		css_put(&memcg->css);