memcg: don't use mem_cgroup_get() when creating a kmemcg cache

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 <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Glauber Costa <[email protected]>
Cc: Johannes Weiner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4c31a21a55be87a1cd7b056aea1bb8de2e97c7b6..80175ded718d95af22e1602e7f5e5974cce5d5f0 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3242,7 +3242,7 @@ void memcg_release_cache(struct kmem_cache *s)
        list_del(&s->memcg_params->list);
        mutex_unlock(&memcg->slab_caches_mutex);
 
-       mem_cgroup_put(memcg);
+       css_put(&memcg->css);
 out:
        kfree(s->memcg_params);
 }
@@ -3402,16 +3402,18 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
 
        mutex_lock(&memcg_cache_mutex);
        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;
@@ -3499,8 +3501,6 @@ 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);
        kfree(cw);
 }