mm/memcg: scanning_global_lru means mem_cgroup_disabled

Although one has to admire the skill with which it has been concealed,
scanning_global_lru(mz) is actually just an interesting way to test
mem_cgroup_disabled().  Too many developer hours have been wasted on
confusing it with global_reclaim(): just use mem_cgroup_disabled().

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Glauber Costa <glommer@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -140,26 +140,16 @@ static bool global_reclaim(struct scan_control *sc)
 {
 	return !sc->target_mem_cgroup;
 }
-
-static bool scanning_global_lru(struct mem_cgroup_zone *mz)
-{
-	return !mz->mem_cgroup;
-}
 #else
 static bool global_reclaim(struct scan_control *sc)
 {
 	return true;
 }
-
-static bool scanning_global_lru(struct mem_cgroup_zone *mz)
-{
-	return true;
-}
 #endif
 
 static struct zone_reclaim_stat *get_reclaim_stat(struct mem_cgroup_zone *mz)
 {
-	if (!scanning_global_lru(mz))
+	if (!mem_cgroup_disabled())
 		return mem_cgroup_get_reclaim_stat(mz->mem_cgroup, mz->zone);
 
 	return &mz->zone->reclaim_stat;
@@ -168,7 +158,7 @@ static struct zone_reclaim_stat *get_reclaim_stat(struct mem_cgroup_zone *mz)
 static unsigned long zone_nr_lru_pages(struct mem_cgroup_zone *mz,
 				       enum lru_list lru)
 {
-	if (!scanning_global_lru(mz))
+	if (!mem_cgroup_disabled())
 		return mem_cgroup_zone_nr_lru_pages(mz->mem_cgroup,
 						    zone_to_nid(mz->zone),
 						    zone_idx(mz->zone),
@@ -1589,7 +1579,7 @@ static int inactive_anon_is_low(struct mem_cgroup_zone *mz)
 	if (!total_swap_pages)
 		return 0;
 
-	if (!scanning_global_lru(mz))
+	if (!mem_cgroup_disabled())
 		return mem_cgroup_inactive_anon_is_low(mz->mem_cgroup,
 						       mz->zone);
 
@@ -1628,7 +1618,7 @@ static int inactive_file_is_low_global(struct zone *zone)
  */
 static int inactive_file_is_low(struct mem_cgroup_zone *mz)
 {
-	if (!scanning_global_lru(mz))
+	if (!mem_cgroup_disabled())
 		return mem_cgroup_inactive_file_is_low(mz->mem_cgroup,
 						       mz->zone);