Re: [PATCH] memcg: revise the position of threshold index while unregistering event

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 5 Apr 2012 16:35:30 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Tue,  6 Mar 2012 20:12:23 +0800
> Sha Zhengju <handai.szj@gmail.com> wrote:
> 
> > From: Sha Zhengju <handai.szj@taobao.com>
> > 
> > Index current_threshold should point to threshold just below or equal to usage.
> > See below:
> > http://www.spinics.net/lists/cgroups/msg00844.html
> 
> I have a bad feeling that I looked at a version of this patch
> yesterday, but I can't find it.

Found it!  Below.

I think we might as well fold "memcg: revise the position of threshold
index while unregistering event" into the below "memcg: make threshold
index in the right position" as a single patch?



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

 mm/memcontrol.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff -puN mm/memcontrol.c~memcg-make-threshold-index-in-the-right-position mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-make-threshold-index-in-the-right-position
+++ a/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;
@@ -4267,7 +4267,7 @@ static void __mem_cgroup_threshold(struc
 	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().
 	 */
@@ -4393,14 +4393,15 @@ static int mem_cgroup_usage_register_eve
 	/* 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 */
_

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