mm: vmscan: remove memcg_shrinker_map_size

Both memcg_shrinker_map_size and shrinker_nr_max is maintained, but
actually the map size can be calculated via shrinker_nr_max, so it seems
unnecessary to keep both.  Remove memcg_shrinker_map_size since
shrinker_nr_max is also used by iterating the bit map.

Link: https://lkml.kernel.org/r/20210311190845.9708-5-shy828301@gmail.comSigned-off-by: Yang Shi <shy828301@gmail.com>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -185,8 +185,12 @@ static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
 #ifdef CONFIG_MEMCG
+static int shrinker_nr_max;
 
-static int memcg_shrinker_map_size;
+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)
 {
@@ -248,7 +252,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
 		return 0;
 
 	down_write(&shrinker_rwsem);
-	size = memcg_shrinker_map_size;
+	size = shrinker_map_size(shrinker_nr_max);
 	for_each_node(nid) {
 		map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
 		if (!map) {
@@ -266,12 +270,13 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
 static int expand_shrinker_maps(int new_id)
 {
 	int size, old_size, ret = 0;
+	int new_nr_max = new_id + 1;
 	struct mem_cgroup *memcg;
 
-	size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
-	old_size = memcg_shrinker_map_size;
+	size = shrinker_map_size(new_nr_max);
+	old_size = shrinker_map_size(shrinker_nr_max);
 	if (size <= old_size)
-		return 0;
+		goto out;
 
 	if (!root_mem_cgroup)
 		goto out;
@@ -290,7 +295,7 @@ static int expand_shrinker_maps(int new_id)
 	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 out:
 	if (!ret)
-		memcg_shrinker_map_size = size;
+		shrinker_nr_max = new_nr_max;
 
 	return ret;
 }
@@ -323,7 +328,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
 
 static DEFINE_IDR(shrinker_idr);
-static int shrinker_nr_max;
 
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 {
@@ -340,8 +344,6 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 			idr_remove(&shrinker_idr, id);
 			goto unlock;
 		}
-
-		shrinker_nr_max = id + 1;
 	}
 	shrinker->id = id;
 	ret = 0;