mm: vmscan: use kvfree_rcu instead of call_rcu

Using kvfree_rcu() to free the old shrinker_maps instead of call_rcu().
We don't have to define a dedicated callback for call_rcu() anymore.

Link: https://lkml.kernel.org/r/20210311190845.9708-6-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -192,11 +192,6 @@ static inline int shrinker_map_size(int nr_items)
 	return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
 }
 
-static void free_shrinker_map_rcu(struct rcu_head *head)
-{
-	kvfree(container_of(head, struct memcg_shrinker_map, rcu));
-}
-
 static int expand_one_shrinker_map(struct mem_cgroup *memcg,
 				   int size, int old_size)
 {
@@ -220,7 +215,7 @@ static int expand_one_shrinker_map(struct mem_cgroup *memcg,
 		memset((void *)new->map + old_size, 0, size - old_size);
 
 		rcu_assign_pointer(pn->shrinker_map, new);
-		call_rcu(&old->rcu, free_shrinker_map_rcu);
+		kvfree_rcu(old, rcu);
 	}
 
 	return 0;