linux-kernel - Re: [PATCH 0/6] Use two zonelists per node instead of multiple zonelists v11r2

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Message-Id: <20071213092338.8b10944c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 13 Dec 2007 09:23:38 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
Cc:	Mel Gorman <mel@....ul.ie>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	rientjes@...gle.com, clameter@....com
Subject: Re: [PATCH 0/6] Use two zonelists per node instead of multiple
 zonelists v11r2

On Wed, 12 Dec 2007 16:32:51 -0500
Lee Schermerhorn <Lee.Schermerhorn@...com> wrote:

> Just this afternoon, I hit a null pointer deref in
> __mem_cgroup_remove_list() [called from mem_cgroup_uncharge() if I can
> trust the stack trace] attempting to unmap a page for migration.  I'm
> just starting to investigate this.
> 
> I'll replace the series I have [~V10] with V11r2 and continue testing in
> anticipation of the day that we can get this into -mm.
> 
Hi, Lee-san.

Could you know what is the caller of page migration ?
system call ? hot removal ? or some new thing ?

Note: 2.6.24-rc4-mm1's cgroup/migration logic.

In 2.6.24-rc4-mm1, in page migration, mem_cgroup_prepare_migration() increments
page_cgroup's refcnt before calling try_to_unmap(). This extra refcnt guarantees 
the page_cgroup's refcnt will not drop to 0 in sequence of
unmap_and_move() -> try_to_unmap() -> page_remove_rmap() -> mem_cgroup_unchage(). 

Thanks,
-Kame

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