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 6EA626B0071 for ; Thu, 25 Mar 2010 05:09:42 -0400 (EDT) Received: from m5.gw.fujitsu.co.jp ([10.0.50.75]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o2P99dU3025501 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Thu, 25 Mar 2010 18:09:39 +0900 Received: from smail (m5 [127.0.0.1]) by outgoing.m5.gw.fujitsu.co.jp (Postfix) with ESMTP id ED13145DE53 for ; Thu, 25 Mar 2010 18:09:38 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (s5.gw.fujitsu.co.jp [10.0.50.95]) by m5.gw.fujitsu.co.jp (Postfix) with ESMTP id BD63645DE4F for ; Thu, 25 Mar 2010 18:09:38 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id 81FF8E18006 for ; Thu, 25 Mar 2010 18:09:38 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.249.87.107]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id 27C301DB8040 for ; Thu, 25 Mar 2010 18:09:35 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages In-Reply-To: <20100325180221.e1d9bae7.kamezawa.hiroyu@jp.fujitsu.com> References: <20100325083235.GF2024@csn.ul.ie> <20100325180221.e1d9bae7.kamezawa.hiroyu@jp.fujitsu.com> Message-Id: <20100325180726.6C89.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Thu, 25 Mar 2010 18:09:34 +0900 (JST) Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: kosaki.motohiro@jp.fujitsu.com, Mel Gorman , 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. But Christoph seems oppose to remove SLAB_DESTROY_BY_RCU. then refcount is meaningless now. I agree you if we will remove SLAB_DESTROY_BY_RCU in the future. refcount is easy understanding than rcu trick. > 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...) agreed. > > 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