On 02/02/2012 06:54 PM, Sha Zhengju wrote:

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

quoted

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

Err.. Sorry for showing inaccurate index position... (may because of the 
mail format)

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

next turn:
     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)

quoted

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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