From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752931Ab0CSJAL (ORCPT ); Fri, 19 Mar 2010 05:00:11 -0400 Received: from gir.skynet.ie ([193.1.99.77]:33849 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751329Ab0CSJAI (ORCPT ); Fri, 19 Mar 2010 05:00:08 -0400 Date: Fri, 19 Mar 2010 08:59:49 +0000 From: Mel Gorman To: KOSAKI Motohiro Cc: Minchan Kim , KAMEZAWA Hiroyuki , Andrew Morton , Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , David Rientjes , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages Message-ID: <20100319085949.GQ12388@csn.ul.ie> References: <20100318094720.872F.A69D9226@jp.fujitsu.com> <20100318111436.GK12388@csn.ul.ie> <20100319152103.876F.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100319152103.876F.A69D9226@jp.fujitsu.com> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 19, 2010 at 03:21:41PM +0900, KOSAKI Motohiro wrote: > > > then, this logic depend on SLAB_DESTROY_BY_RCU, not refcount. > > > So, I think we don't need your [1/11] patch. > > > > > > Am I missing something? > > > > > > > The refcount is still needed. The anon_vma might be valid, but the > > refcount is what ensures that the anon_vma is not freed and reused. > > please please why do we need both mechanism. now cristoph is very busy and I am > de fact reviewer of page migration and mempolicy code. I really hope to understand > your patch. > As in, why not drop the RCU protection of anon_vma altogeter? Mainly, because I think it would be reaching too far for this patchset and it should be done as a follow-up. Putting the ref-count everywhere will change the cache-behaviour of anon_vma more than I'd like to slip into a patchset like this. Secondly, Christoph mentions that SLAB_DESTROY_BY_RCU is used to keep anon_vma cache-hot. For these reasons, removing RCU from these paths and adding the refcount in others is a patch that should stand on its own. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 19C286B00BE for ; Fri, 19 Mar 2010 05:00:09 -0400 (EDT) Date: Fri, 19 Mar 2010 08:59:49 +0000 From: Mel Gorman Subject: Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages Message-ID: <20100319085949.GQ12388@csn.ul.ie> References: <20100318094720.872F.A69D9226@jp.fujitsu.com> <20100318111436.GK12388@csn.ul.ie> <20100319152103.876F.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100319152103.876F.A69D9226@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Minchan Kim , KAMEZAWA Hiroyuki , 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 Fri, Mar 19, 2010 at 03:21:41PM +0900, KOSAKI Motohiro wrote: > > > then, this logic depend on SLAB_DESTROY_BY_RCU, not refcount. > > > So, I think we don't need your [1/11] patch. > > > > > > Am I missing something? > > > > > > > The refcount is still needed. The anon_vma might be valid, but the > > refcount is what ensures that the anon_vma is not freed and reused. > > please please why do we need both mechanism. now cristoph is very busy and I am > de fact reviewer of page migration and mempolicy code. I really hope to understand > your patch. > As in, why not drop the RCU protection of anon_vma altogeter? Mainly, because I think it would be reaching too far for this patchset and it should be done as a follow-up. Putting the ref-count everywhere will change the cache-behaviour of anon_vma more than I'd like to slip into a patchset like this. Secondly, Christoph mentions that SLAB_DESTROY_BY_RCU is used to keep anon_vma cache-hot. For these reasons, removing RCU from these paths and adding the refcount in others is a patch that should stand on its own. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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