[RFC][PATCH 6/7] memcg: don't need to get a reference to the parent

[Li Zefan]

The cgroup core guarantees it's always safe to access the parent.

Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
---
 mm/memcontrol.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ad576e8..45129cd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6124,12 +6124,8 @@ static void mem_cgroup_get(struct mem_cgroup *memcg)
 
 static void __mem_cgroup_put(struct mem_cgroup *memcg, int count)
 {
-	if (atomic_sub_and_test(count, &memcg->refcnt)) {
-		struct mem_cgroup *parent = parent_mem_cgroup(memcg);
+	if (atomic_sub_and_test(count, &memcg->refcnt))
 		call_rcu(&memcg->rcu_freeing, free_rcu);
-		if (parent)
-			mem_cgroup_put(parent);
-	}
 }
 
 static void mem_cgroup_put(struct mem_cgroup *memcg)
@@ -6229,14 +6225,6 @@ mem_cgroup_css_online(struct cgroup *cont)
 		res_counter_init(&memcg->res, &parent->res);
 		res_counter_init(&memcg->memsw, &parent->memsw);
 		res_counter_init(&memcg->kmem, &parent->kmem);
-
-		/*
-		 * We increment refcnt of the parent to ensure that we can
-		 * safely access it on res_counter_charge/uncharge.
-		 * This refcnt will be decremented when freeing this
-		 * mem_cgroup(see mem_cgroup_put).
-		 */
-		mem_cgroup_get(parent);
 	} else {
 		res_counter_init(&memcg->res, NULL);
 		res_counter_init(&memcg->memsw, NULL);
-- 
1.8.0.2
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