From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 18B4E6B0071 for ; Thu, 25 Mar 2010 05:06:09 -0400 (EDT) Received: from m1.gw.fujitsu.co.jp ([10.0.50.71]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o2P966dB024253 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Thu, 25 Mar 2010 18:06:06 +0900 Received: from smail (m1 [127.0.0.1]) by outgoing.m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 5225B45DE55 for ; Thu, 25 Mar 2010 18:06:06 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (s1.gw.fujitsu.co.jp [10.0.50.91]) by m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 2763545DE59 for ; Thu, 25 Mar 2010 18:06:06 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id D3AA2E78006 for ; Thu, 25 Mar 2010 18:06:05 +0900 (JST) Received: from m105.s.css.fujitsu.com (m105.s.css.fujitsu.com [10.249.87.105]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id 746EBE38004 for ; Thu, 25 Mar 2010 18:06:05 +0900 (JST) Date: Thu, 25 Mar 2010 18:02:21 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages Message-Id: <20100325180221.e1d9bae7.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100325083235.GF2024@csn.ul.ie> References: <20100319152103.876F.A69D9226@jp.fujitsu.com> <20100319085949.GQ12388@csn.ul.ie> <20100325095349.944E.A69D9226@jp.fujitsu.com> <20100325083235.GF2024@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: KOSAKI Motohiro , Minchan Kim , Andrew Morton , Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , David Rientjes , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, 25 Mar 2010 08:32:35 +0000 Mel Gorman wrote: > On Thu, Mar 25, 2010 at 11:49:23AM +0900, KOSAKI Motohiro wrote: > > > On Fri, Mar 19, 2010 at 03:21:41PM +0900, KOSAKI Motohiro wrote: > > Hmmm... > > I haven't understand your mention because I guess I was wrong. > > > > probably my last question was unclear. I mean, > > > > 1) If we still need SLAB_DESTROY_BY_RCU, why do we need to add refcount? > > Which difference is exist between normal page migration and compaction? > > The processes typically calling migration today own the page they are moving > and is not going to exit unexpectedly during migration. > > > 2) If we added refcount, which race will solve? > > > > The process exiting and the last anon_vma being dropped while compaction > is running. This can be reliably triggered with compaction. > > > IOW, Is this patch fix old issue or compaction specific issue? > > > > Strictly speaking, it's an old issue but in practice it's impossible to > trigger because the process migrating always owns the page. Compaction > moves pages belonging to arbitrary processes. > Kosaki-san, IIUC, the race in memory-hotunplug was fixed by this patch [2/11]. But, this behavior of unmap_and_move() requires access to _freed_ objects (spinlock). Even if it's safe because of SLAB_DESTROY_BY_RCU, it't not good habit in general. After direct compaction, page-migration will be one of "core" code of memory management. Then, I agree to patch [1/11] as our direction for keeping sanity and showing direction to more updates. Maybe adding refcnt and removing RCU in futuer is good. IMHO, pushing this patch [2/11] as "BUGFIX" independent of this set and adding anon_vma->refcnt [1/11] and [3/11] in 1st Direct-compaction patch series to show the direction will makse sense. (I think merging 1/11 and 3/11 will be okay...) 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