memcg: soft limit reclaim should end at limit not below

Soft limit reclaim continues until the usage is below the current soft
limit, but the documented semantics are actually that soft limit reclaim
will push usage back until the soft limits are met again.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/res_counter.h

@@ -139,7 +139,7 @@ static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
 
 static inline bool res_counter_soft_limit_check_locked(struct res_counter *cnt)
 {
-	if (cnt->usage < cnt->soft_limit)
+	if (cnt->usage <= cnt->soft_limit)
 		return true;
 
 	return false;
@@ -202,7 +202,7 @@ static inline bool res_counter_check_margin(struct res_counter *cnt,
 	return ret;
 }
 
-static inline bool res_counter_check_under_soft_limit(struct res_counter *cnt)
+static inline bool res_counter_check_within_soft_limit(struct res_counter *cnt)
 {
 	bool ret;
 	unsigned long flags;

mm/memcontrol.c

@@ -1477,7 +1477,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
 			return ret;
 		total += ret;
 		if (check_soft) {
-			if (res_counter_check_under_soft_limit(&root_mem->res))
+			if (res_counter_check_within_soft_limit(&root_mem->res))
 				return total;
 		} else if (mem_cgroup_check_under_limit(root_mem))
 			return 1 + total;