memcg: make threshold index in the right position

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

For example:
now:
	threshold array:  3  [5]  7  9   (usage = 6, [index] = 5)

next turn (after calling __mem_cgroup_threshold):
	threshold array:  3   5  [7]  9   (usage = 7, [index] = 7)

after registering a new event (threshold = 10):
	threshold array:  3  [5]  7  9  10 (usage = 7, [index] = 5)

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ec436ffb12706e171ac91f402bdd5244c74a0ca6..ed0d707094d82c18e3f17b91e2bcfceafe138332 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -181,7 +181,7 @@ 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;
@@ -4472,7 +4472,7 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
        usage = mem_cgroup_usage(memcg, swap);
 
        /*
-        * current_threshold points to threshold just below usage.
+        * current_threshold points to threshold just below or equal to usage.
         * If it's not true, a threshold was crossed after last
         * call of __mem_cgroup_threshold().
         */
@@ -4598,14 +4598,15 @@ 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 */