[PATCH] memcg: make threshold index in the right position

[Sha Zhengju <handai.szj@gmail.com>]

From: Sha Zhengju <handai.szj@taobao.com>

Index current_threshold may point to threshold that just equal to
usage after __mem_cgroup_threshold is triggerd. But after registering
a new event, it will change (pointing to threshold just below usage).
So make it consistent here.

Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
---
 mm/memcontrol.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 22d94f5..79f4a58 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -183,7 +183,7 @@ struct mem_cgroup_threshold {
 
 /* For threshold */
 struct mem_cgroup_threshold_ary {
-	/* An array index points to threshold just below usage. */
+	/* An array index points to threshold just below or equal to usage. */
 	int current_threshold;
 	/* Size of entries[] */
 	unsigned int size;
@@ -4319,14 +4319,15 @@ static int mem_cgroup_usage_register_event(struct cgroup *cgrp,
 	/* Find current threshold */
 	new->current_threshold = -1;
 	for (i = 0; i < size; i++) {
-		if (new->entries[i].threshold < usage) {
+		if (new->entries[i].threshold <= usage) {
 			/*
 			 * new->current_threshold will not be used until
 			 * rcu_assign_pointer(), so it's safe to increment
 			 * it here.
 			 */
 			++new->current_threshold;
-		}
+		} else
+			break;
 	}
 
 	/* Free old spare buffer and save old primary buffer as spare */
-- 
1.7.4.1

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