slab: use css id for naming per memcg caches

Currently, we use mem_cgroup->kmemcg_id to guarantee kmem_cache->name
uniqueness.  This is correct, because kmemcg_id is only released on css
free after destroying all per memcg caches.

However, I am going to change that and release kmemcg_id on css offline,
because it is not wise to keep it for so long, wasting valuable entries of
memcg_cache_params->memcg_caches arrays.  Therefore, to preserve cache
name uniqueness, let us switch to css->id.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 989784b..6087b1f 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -488,6 +488,7 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
                             struct kmem_cache *root_cache)
 {
        static char memcg_name_buf[NAME_MAX + 1]; /* protected by slab_mutex */
+       struct cgroup_subsys_state *css = mem_cgroup_css(memcg);
        struct memcg_cache_array *arr;
        struct kmem_cache *s = NULL;
        char *cache_name;
@@ -510,10 +511,9 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
        if (arr->entries[idx])
                goto out_unlock;
 
-       cgroup_name(mem_cgroup_css(memcg)->cgroup,
-                   memcg_name_buf, sizeof(memcg_name_buf));
+       cgroup_name(css->cgroup, memcg_name_buf, sizeof(memcg_name_buf));
        cache_name = kasprintf(GFP_KERNEL, "%s(%d:%s)", root_cache->name,
-                              idx, memcg_name_buf);
+                              css->id, memcg_name_buf);
        if (!cache_name)
                goto out_unlock;