[PATCH v4 4/9] memcg: don't use mem_cgroup_get() when creating akmemcg cache

From: Li Zefan
Date: Thu Jun 13 2013 - 21:58:50 EST

Use css_get()/css_put() instead of mem_cgroup_get()/mem_cgroup_put().

There are two things being done in the current code:

First, we acquired a css_ref to make sure that the underlying cgroup
would not go away. That is a short lived reference, and it is put as
soon as the cache is created.

At this point, we acquire a long-lived per-cache memcg reference count
to guarantee that the memcg will still be alive.

so it is:

enqueue: css_get
create : memcg_get, css_put
destroy: memcg_put

So we only need to get rid of the memcg_get, change the memcg_put to
css_put, and get rid of the now extra css_put.

(This changelog is mostly written by Glauber)

Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
mm/memcontrol.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a8e8d2a..466c595 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3252,7 +3252,7 @@ void memcg_release_cache(struct kmem_cache *s)

- mem_cgroup_put(memcg);
+ css_put(&memcg->css);
@@ -3412,16 +3412,18 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,

new_cachep = cachep->memcg_params->memcg_caches[idx];
- if (new_cachep)
+ if (new_cachep) {
+ css_put(&memcg->css);
goto out;
+ }

new_cachep = kmem_cache_dup(memcg, cachep);
if (new_cachep == NULL) {
new_cachep = cachep;
+ css_put(&memcg->css);
goto out;

- mem_cgroup_get(memcg);
atomic_set(&new_cachep->memcg_params->nr_pages , 0);

cachep->memcg_params->memcg_caches[idx] = new_cachep;
@@ -3509,8 +3511,6 @@ static void memcg_create_cache_work_func(struct work_struct *w)

cw = container_of(w, struct create_work, work);
memcg_create_kmem_cache(cw->memcg, cw->cachep);
- /* Drop the reference gotten when we enqueued. */
- css_put(&cw->memcg->css);


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