[PATCH v4 7/9] memcg: don't need to get a reference to the parent

From: Li Zefan
Date: Thu Jun 13 2013 - 21:59:09 EST


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

v2:
- added a comment in mem_cgroup_put() as suggested by Michal
- removed mem_cgroup_get(), otherwise gcc will warn that it's not used

Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
mm/memcontrol.c | 19 +++----------------
1 file changed, 3 insertions(+), 16 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a63d9f1..443fb45 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -513,7 +513,6 @@ enum res_type {
*/
static DEFINE_MUTEX(memcg_create_mutex);

-static void mem_cgroup_get(struct mem_cgroup *memcg);
static void mem_cgroup_put(struct mem_cgroup *memcg);

static inline
@@ -6210,19 +6209,10 @@ static void free_rcu(struct rcu_head *rcu_head)
schedule_work(&memcg->work_freeing);
}

-static void mem_cgroup_get(struct mem_cgroup *memcg)
-{
- atomic_inc(&memcg->refcnt);
-}
-
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)
@@ -6325,12 +6315,9 @@ mem_cgroup_css_online(struct cgroup *cont)
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).
+ * No need to take a reference to the parent because cgroup
+ * core guarantees its existence.
*/
- mem_cgroup_get(parent);
} else {
res_counter_init(&memcg->res, NULL);
res_counter_init(&memcg->memsw, NULL);
--
1.8.0.2
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/