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@xxxxxxx> Reviewed-by: Tejun Heo <tj@xxxxxxxxxx> --- mm/memcontrol.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 07d92b8..916132a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -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); -- 1.7.10.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>