memcg: add mem_cgroup_same_or_subtree() helper

We are checking whether a given two groups are same or at least in the
same subtree of a hierarchy at several places.  Let's make a helper for
it to make code easier to read.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 26 insertions, 25 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index af920d0f9025..79f23a189941 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1108,6 +1108,21 @@ void mem_cgroup_move_lists(struct page *page,
         mem_cgroup_add_lru_list(page, to);
 }
 
+/*
+ * Checks whether given mem is same or in the root_mem's
+ * hierarchy subtree
+ */
+static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_mem,
+                struct mem_cgroup *mem)
+{
+        if (root_mem != mem) {
+                return (root_mem->use_hierarchy &&
+                        css_is_ancestor(&mem->css, &root_mem->css));
+        }
+
+        return true;
+}
+
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
 {
         int ret;
@@ -1127,10 +1142,7 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
          * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
          * hierarchy(even if use_hierarchy is disabled in "mem").
          */
-        if (mem->use_hierarchy)
-                ret = css_is_ancestor(&curr->css, &mem->css);
-        else
-                ret = (curr == mem);
+        ret = mem_cgroup_same_or_subtree(mem, curr);
         css_put(&curr->css);
         return ret;
 }
@@ -1369,10 +1381,9 @@ static bool mem_cgroup_under_move(struct mem_cgroup *mem)
         to = mc.to;
         if (!from)
                 goto unlock;
-        if (from == mem || to == mem
-            || (mem->use_hierarchy && css_is_ancestor(&from->css, &mem->css))
-            || (mem->use_hierarchy && css_is_ancestor(&to->css, &mem->css)))
-                ret = true;
+
+        ret = mem_cgroup_same_or_subtree(mem, from)
+                || mem_cgroup_same_or_subtree(mem, to);
 unlock:
         spin_unlock(&mc.lock);
         return ret;
@@ -1915,25 +1926,20 @@ struct oom_wait_info {
 static int memcg_oom_wake_function(wait_queue_t *wait,
         unsigned mode, int sync, void *arg)
 {
-        struct mem_cgroup *wake_mem = (struct mem_cgroup *)arg;
+        struct mem_cgroup *wake_mem = (struct mem_cgroup *)arg,
+                          *oom_wait_mem;
         struct oom_wait_info *oom_wait_info;
 
         oom_wait_info = container_of(wait, struct oom_wait_info, wait);
+        oom_wait_mem = oom_wait_info->mem;
 
-        if (oom_wait_info->mem == wake_mem)
-                goto wakeup;
-        /* if no hierarchy, no match */
-        if (!oom_wait_info->mem->use_hierarchy || !wake_mem->use_hierarchy)
-                return 0;
         /*
          * Both of oom_wait_info->mem and wake_mem are stable under us.
          * Then we can use css_is_ancestor without taking care of RCU.
          */
-        if (!css_is_ancestor(&oom_wait_info->mem->css, &wake_mem->css) &&
-            !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css))
+        if (!mem_cgroup_same_or_subtree(oom_wait_mem, wake_mem)
+                        && !mem_cgroup_same_or_subtree(wake_mem, oom_wait_mem))
                 return 0;
-
-wakeup:
         return autoremove_wake_function(wait, mode, sync, arg);
 }
 
@@ -2178,13 +2184,8 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync)
                 mem = stock->cached;
                 if (!mem || !stock->nr_pages)
                         continue;
-                if (mem != root_mem) {
-                        if (!root_mem->use_hierarchy)
-                                continue;
-                        /* check whether "mem" is under tree of "root_mem" */
-                        if (!css_is_ancestor(&mem->css, &root_mem->css))
-                                continue;
-                }
+                if (!mem_cgroup_same_or_subtree(root_mem, mem))
+                        continue;
                 if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
                         if (cpu == curcpu)
                                 drain_local_stock(&stock->work);