On 02/02/2012 06:14 PM, Kirill A. Shutemov wrote:

On Thu, Feb 02, 2012 at 05:45:19PM +0800, Sha Zhengju wrote:

quoted

From: Sha Zhengju<redacted>

Index current_threshold may point to threshold that just equal to
usage after __mem_cgroup_threshold is triggerd.

I don't see it. Could you describe conditions?

It is because of the following code path in __mem_cgroup_threshold:
{
     ...
         i = t->current_threshold;

         for (; i >= 0 && unlikely(t->entries[i].threshold > usage); i--)
                 eventfd_signal(t->entries[i].eventfd, 1);
         i++;

         for (; i < t->size && unlikely(t->entries[i].threshold <= 
usage); i++)
                 eventfd_signal(t->entries[i].eventfd, 1);

         t->current_threshold = i - 1;
     ...
}

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

next turn:
     threshold array:  3  5  7  9   (usage = 7)
                                        ^
                                     index

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

quoted

But after registering
a new event, it will change (pointing to threshold just below usage).
So make it consistent here.

Cc: KAMEZAWA Hiroyuki<redacted>
Cc: Kirill A. Shutemov<redacted>
Signed-off-by: Sha Zhengju<redacted>
---
  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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