linux-kernel - [mmotm][BUGFIX][PATCH] memcg: fix softlimit css refcnt handling(yet another one)

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Date:	Mon, 7 Sep 2009 08:04:03 +0900
From:	Daisuke Nishimura <d-nishimura@....biglobe.ne.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	d-nishimura@....biglobe.ne.jp,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: [mmotm][BUGFIX][PATCH] memcg: fix softlimit css refcnt handling(yet
 another one)

On Fri, 4 Sep 2009 19:07:26 +0900
Daisuke Nishimura <d-nishimura@....biglobe.ne.jp> wrote:

> On Fri, 4 Sep 2009 16:37:58 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> 
> > On Fri, 4 Sep 2009 15:40:50 +0900
> > Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> > > > Ah, one more question. What memory.usage_in_bytes shows in that case ?
> > > > If not zero, charge/uncharge coalescing is guilty.
> > > > 
> > > usage_in_bytes is 0.
> > > I've confirmed by crash command that the mem_cgroup has extra ref counts.
> > > 
> > > I'll dig more..
> > > 
> > BTW, do you use softlimit ? I found this but...Hmm
> > 
> No.
> I'm sorry I can't access my machine, so can't test this.
> 
> 
> But I think this patch itself is needed and looks good.
> 
I've found the cause of the issue.

Andrew, could you add this one after KAMEZAWA-san's
memory-controller-soft-limit-reclaim-on-contention-v9-fix-softlimit-css-refcnt-handling.patch ?

===
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>

refcount of the "victim" should be decremented before exiting the loop.

Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
---
 mm/memcontrol.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ac51294..011aba6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1133,8 +1133,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
 				 * anything, it might because there are
 				 * no reclaimable pages under this hierarchy
 				 */
-				if (!check_soft || !total)
+				if (!check_soft || !total) {
+					css_put(&victim->css);
 					break;
+				}
 				/*
 				 * We want to do more targetted reclaim.
 				 * excess >> 2 is not to excessive so as to
@@ -1142,8 +1144,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
 				 * coming back to reclaim from this cgroup
 				 */
 				if (total >= (excess >> 2) ||
-					(loop > MEM_CGROUP_MAX_RECLAIM_LOOPS))
+					(loop > MEM_CGROUP_MAX_RECLAIM_LOOPS)) {
+					css_put(&victim->css);
 					break;
+				}
 			}
 		}
 		if (!mem_cgroup_local_usage(&victim->stat)) {
--
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