mm: swap: use mem_cgroup_is_root() instead of deferencing css->parent

mem_cgroup_is_root() is the preferred API to check if memcg is root or
not.  Use it instead of deferencing css->parent.

Link: http://lkml.kernel.org/r/1547232913-118148-1-git-send-email-yang.shi@linux.alibaba.com
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Tim Chen <tim.c.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 622025a..649529b 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -625,7 +625,7 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
                return vm_swappiness;
 
        /* root ? */
-       if (mem_cgroup_disabled() || !memcg->css.parent)
+       if (mem_cgroup_disabled() || mem_cgroup_is_root(memcg))
                return vm_swappiness;
 
        return memcg->swappiness;