linux-kernel - [mmotm][BUGFIX][PATCH] memcg: fix softlimit css refcnt handling.

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Message-Id: <20090904163758.a5604fee.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 4 Sep 2009 16:37:58 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
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>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: [mmotm][BUGFIX][PATCH] memcg: fix softlimit css refcnt handling.

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

==
SoftLimit tree 'find next one' loop uses next_mz to remember
next one to be visited if reclaimd==0.
But css'refcnt handling for next_mz is not enough and it makes
css->refcnt leak.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>


---
 mm/memcontrol.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

Index: mmotm-2.6.31-Aug27/mm/memcontrol.c
===================================================================
--- mmotm-2.6.31-Aug27.orig/mm/memcontrol.c
+++ mmotm-2.6.31-Aug27/mm/memcontrol.c
@@ -2261,6 +2261,8 @@ unsigned long mem_cgroup_soft_limit_recl
 		if (!reclaimed) {
 			do {
 				/*
+				 * Loop until we find yet another one.
+				 *
 				 * By the time we get the soft_limit lock
 				 * again, someone might have aded the
 				 * group back on the RB tree. Iterate to
@@ -2271,7 +2273,12 @@ unsigned long mem_cgroup_soft_limit_recl
 				 */
 				next_mz =
 				__mem_cgroup_largest_soft_limit_node(mctz);
-			} while (next_mz == mz);
+				if (next_mz == mz) {
+					css_put(&next_mz->mem->css);
+					next_mz = NULL;
+				} else /* next_mz == NULL or other memcg */
+					break;
+			} while (1);
 		}
 		mz->usage_in_excess =
 			res_counter_soft_limit_excess(&mz->mem->res);
@@ -2299,6 +2306,8 @@ unsigned long mem_cgroup_soft_limit_recl
 			loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
 			break;
 	} while (!nr_reclaimed);
+	if (next_mz)
+		css_put(&next_mz->mem->css);
 	return nr_reclaimed;
 }
 

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