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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>
hifive-unleashed-5.1
Michal Hocko 2012-10-26 13:37:29 +02:00 committed by Tejun Heo
parent c26251f9f0
commit d842301181
1 changed files with 3 additions and 3 deletions
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6
mm/memcontrol.c
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@ -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);