[Fix Glauber's new address]

On Thu 13-06-13 17:53:19, Michal Hocko wrote:

On Thu 13-06-13 17:12:55, Li Zefan wrote:

quoted

Sorry for updating the patchset so late.

I've made some changes for the memory barrier thing, and I agree with
Michal that there can be improvement but can be a separate patch.

If this version is ok for everyone, I'll send the whole patchset out
to Andrew.

=========================

Use css_get/put instead of mem_cgroup_get/put.

We can't do a simple replacement, because here mem_cgroup_put()
is called during mem_cgroup_css_free(), while mem_cgroup_css_free()
won't be called until css refcnt goes down to 0.

Instead we increment css refcnt in mem_cgroup_css_offline(), and
then check if there's still kmem charges. If not, css refcnt will
be decremented immediately, 

quoted

otherwise the refcnt won't be decremented when kmem charges goes down
to 0.

This is a bit confusing. What about "otherwise the css refcount will be
released after the last kmem allocation is uncharged."

quoted

v3:
- changed wmb() to smp_smb(), and moved it to memcg_kmem_mark_dead(),
  and added comment.

v2:
- added wmb() in kmem_cgroup_css_offline(), pointed out by Michal
- revised comments as suggested by Michal
- fixed to check if kmem is activated in kmem_cgroup_css_offline()

Signed-off-by: Li Zefan <redacted>
Acked-by: Michal Hocko <redacted>
Acked-by: KAMEZAWA Hiroyuki <redacted>
---
 mm/memcontrol.c | 70 ++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 45 insertions(+), 25 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 466c595..76dcd0e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -416,6 +416,11 @@ static void memcg_kmem_clear_activated(struct mem_cgroup *memcg)
 
 static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
 {
+	/*
+	 * We need to call css_get() first, because memcg_uncharge_kmem()
+	 * will call css_put() if it sees the memcg is dead.
+	 */
+	smb_wmb();
 	if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
 		set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);

I do not feel strongly about that but maybe open coding this in
mem_cgroup_css_offline would be even better. There is only single caller
and there is smaller chance somebody will use the function incorrectly
later on.

So I leave the decision on you because this doesn't matter much.

[...]
-- 
Michal Hocko
SUSE Labs
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-- 
Michal Hocko
SUSE Labs

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