linux-kernel - Re: + memcg-remove-refcnt-from-page

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Message-Id: <20080520153525.5b21b89c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 20 May 2008 15:35:25 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, balbir@...ibm.com,
	ebiederm@...ssion.com, hugh@...itas.com, lizf@...fujitsu.com,
	menage@...gle.com, rientjes@...gle.com, xemul@...nvz.org,
	yamamoto@...inux.co.jp
Subject: Re: + memcg-remove-refcnt-from-page_cgroup.patch added to -mm tree

hi, I found a bug in this patch. (A fix is attached below.)

On Thu, 15 May 2008 19:53:17 -0700
akpm@...ux-foundation.org wrote:

> +/* remove redundant charge if migration failed*/
>  void mem_cgroup_end_migration(struct page *newpage)
>  {
> -	mem_cgroup_uncharge_page(newpage);
> +	/* At success, page->mapping is not NULL */
> +	if (newpage->mapping)
> +		__mem_cgroup_uncharge_common(newpage,
> +					 MEM_CGROUP_CHARGE_TYPE_FORCE);
>  }
>  

Should be if (!newpage->mapping). Maybe a typo in restructuring...

Sorry.
-Kame
==
This rollback should be done at failure.

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

---
 mm/memcontrol.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: mm-2.6.26-rc2-mm1/mm/memcontrol.c
===================================================================
--- mm-2.6.26-rc2-mm1.orig/mm/memcontrol.c
+++ mm-2.6.26-rc2-mm1/mm/memcontrol.c
@@ -760,8 +760,8 @@ int mem_cgroup_prepare_migration(struct 
 /* remove redundant charge if migration failed*/
 void mem_cgroup_end_migration(struct page *newpage)
 {
-	/* At success, page->mapping is not NULL */
-	if (newpage->mapping)
+	/* At success, page->mapping is not NULL and nothing to do. */
+	if (!newpage->mapping)
 		__mem_cgroup_uncharge_common(newpage,
 					 MEM_CGROUP_CHARGE_TYPE_FORCE);
 }

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