slab: reorganize memcg_cache_params

We're going to change how memcg caches are iterated.  In preparation,
clean up and reorganize memcg_cache_params.

* The shared ->list is replaced by ->children in root and
  ->children_node in children.

* ->is_root_cache is removed.  Instead ->root_cache is moved out of
  the child union and now used by both root and children.  NULL
  indicates root cache.  Non-NULL a memcg one.

This patch doesn't cause any observable behavior changes.

Link: http://lkml.kernel.org/r/20170117235411.9408-5-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 9 deletions

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 4c5363566815..1f611ba00f1d 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -545,22 +545,37 @@ struct memcg_cache_array {
  * array to be accessed without taking any locks, on relocation we free the old
  * version only after a grace period.
  *
- * Child caches will hold extra metadata needed for its operation. Fields are:
+ * Root and child caches hold different metadata.
  *
- * @memcg: pointer to the memcg this cache belongs to
- * @root_cache: pointer to the global, root cache, this cache was derived from
+ * @root_cache:	Common to root and child caches.  NULL for root, pointer to
+ *		the root cache for children.
  *
- * Both root and child caches of the same kind are linked into a list chained
- * through @list.
+ * The following fields are specific to root caches.
+ *
+ * @memcg_caches: kmemcg ID indexed table of child caches.  This table is
+ *		used to index child cachces during allocation and cleared
+ *		early during shutdown.
+ *
+ * @children:	List of all child caches.  While the child caches are also
+ *		reachable through @memcg_caches, a child cache remains on
+ *		this list until it is actually destroyed.
+ *
+ * The following fields are specific to child caches.
+ *
+ * @memcg:	Pointer to the memcg this cache belongs to.
+ *
+ * @children_node: List node for @root_cache->children list.
  */
 struct memcg_cache_params {
-	bool is_root_cache;
-	struct list_head list;
+	struct kmem_cache *root_cache;
 	union {
-		struct memcg_cache_array __rcu *memcg_caches;
+		struct {
+			struct memcg_cache_array __rcu *memcg_caches;
+			struct list_head children;
+		};
 		struct {
 			struct mem_cgroup *memcg;
-			struct kmem_cache *root_cache;
+			struct list_head children_node;
 		};
 	};
 };