[PATCH] mm: memcg: fix obsolete code comments

[Roman Gushchin <guro@fb.com>]

This patch fixes/removes some obsolete comments in the code related
to the kernel memory accounting:
- kmem_cache->memcg_params.memcg_caches has been removed
  by commit 9855609bde03 ("mm: memcg/slab: use a single set of
  kmem_caches for all accounted allocations")
- memcg->kmemcg_id is not used as a gate for kmem accounting since
  commit 0b8f73e10428 ("mm: memcontrol: clean up alloc, online,
  offline, free functions")

Signed-off-by: Roman Gushchin <guro@fb.com>
---
 include/linux/memcontrol.h | 6 ++----
 mm/memcontrol.c            | 6 ------
 2 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 20108e426f84..01099dfa839c 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -310,7 +310,6 @@ struct mem_cgroup {
 	int			tcpmem_pressure;
 
 #ifdef CONFIG_MEMCG_KMEM
-        /* Index in the kmem_cache->memcg_params.memcg_caches array */
 	int kmemcg_id;
 	enum memcg_kmem_state kmem_state;
 	struct obj_cgroup __rcu *objcg;
@@ -1641,9 +1640,8 @@ static inline void memcg_kmem_uncharge_page(struct page *page, int order)
 }
 
 /*
- * helper for accessing a memcg's index. It will be used as an index in the
- * child cache array in kmem_cache, and also to derive its name. This function
- * will return -1 when this is not a kmem-limited memcg.
+ * A helper for accessing memcg's kmem_id, used for getting
+ * corresponding LRU lists.
  */
 static inline int memcg_cache_id(struct mem_cgroup *memcg)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 69a2893a6455..62bbd48d8445 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3680,12 +3680,6 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
 
 	static_branch_enable(&memcg_kmem_enabled_key);
 
-	/*
-	 * A memory cgroup is considered kmem-online as soon as it gets
-	 * kmemcg_id. Setting the id after enabling static branching will
-	 * guarantee no one starts accounting before all call sites are
-	 * patched.
-	 */
 	memcg->kmemcg_id = memcg_id;
 	memcg->kmem_state = KMEM_ONLINE;
 
-- 
2.26.2