From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 13 Dec 2007 09:23:38 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 0/6] Use two zonelists per node instead of multiple zonelists v11r2 Message-Id: <20071213092338.8b10944c.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <1197495172.5029.62.camel@localhost> References: <20071211202157.1961.27940.sendpatchset@skynet.skynet.ie> <1197495172.5029.62.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Lee Schermerhorn Cc: Mel Gorman , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, rientjes@google.com, clameter@sgi.com List-ID: On Wed, 12 Dec 2007 16:32:51 -0500 Lee Schermerhorn 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org