sl[au]b: charge slabs to kmemcg explicitly

We have only a few places where we actually want to charge kmem so
instead of intruding into the general page allocation path with
__GFP_KMEMCG it's better to explictly charge kmem there.  All kmem
charges will be easier to follow that way.

This is a step towards removing __GFP_KMEMCG.  It removes __GFP_KMEMCG
from memcg caches' allocflags.  Instead it makes slab allocation path
call memcg_charge_kmem directly getting memcg to charge from the cache's
memcg params.

This also eliminates any possibility of misaccounting an allocation
going from one memcg's cache to another memcg, because now we always
charge slabs against the memcg the cache belongs to.  That's why this
patch removes the big comment to memcg_kmem_get_cache.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 11 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index b569b8be5c5..96e5d2573eb 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -506,6 +506,9 @@ void memcg_update_array_size(int num_groups);
 struct kmem_cache *
 __memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp);
 
+int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size);
+void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size);
+
 void mem_cgroup_destroy_cache(struct kmem_cache *cachep);
 int __kmem_cache_destroy_memcg_children(struct kmem_cache *s);
 
@@ -583,17 +586,7 @@ memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
  * @cachep: the original global kmem cache
  * @gfp: allocation flags.
  *
- * This function assumes that the task allocating, which determines the memcg
- * in the page allocator, belongs to the same cgroup throughout the whole
- * process.  Misacounting can happen if the task calls memcg_kmem_get_cache()
- * while belonging to a cgroup, and later on changes. This is considered
- * acceptable, and should only happen upon task migration.
- *
- * Before the cache is created by the memcg core, there is also a possible
- * imbalance: the task belongs to a memcg, but the cache being allocated from
- * is the global cache, since the child cache is not yet guaranteed to be
- * ready. This case is also fine, since in this case the GFP_KMEMCG will not be
- * passed and the page allocator will not attempt any cgroup accounting.
+ * All memory allocated from a per-memcg cache is charged to the owner memcg.
  */
 static __always_inline struct kmem_cache *
 memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)