From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756903Ab0LISRc (ORCPT ); Thu, 9 Dec 2010 13:17:32 -0500 Received: from mx1.redhat.com ([209.132.183.28]:9548 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756561Ab0LISRa (ORCPT ); Thu, 9 Dec 2010 13:17:30 -0500 Date: Thu, 9 Dec 2010 19:15:53 +0100 From: Andrea Arcangeli To: Mel Gorman Cc: linux-mm@kvack.org, Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, Marcelo Tosatti , Adam Litke , Avi Kivity , Hugh Dickins , Rik van Riel , Dave Hansen , Benjamin Herrenschmidt , Ingo Molnar , Mike Travis , KAMEZAWA Hiroyuki , Christoph Lameter , Chris Wright , bpicco@redhat.com, KOSAKI Motohiro , Balbir Singh , "Michael S. Tsirkin" , Peter Zijlstra , Johannes Weiner , Daisuke Nishimura , Chris Mason , Borislav Petkov Subject: Re: [PATCH 45 of 66] remove PG_buddy Message-ID: <20101209181553.GG19131@random.random> References: <85c897773782cdde8b69.1288798100@v2.random> <20101118160801.GA8135@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101118160801.GA8135@csn.ul.ie> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 18, 2010 at 04:08:01PM +0000, Mel Gorman wrote: > On Wed, Nov 03, 2010 at 04:28:20PM +0100, Andrea Arcangeli wrote: > > From: Andrea Arcangeli > > > > PG_buddy can be converted to _mapcount == -2. So the PG_compound_lock can be > > added to page->flags without overflowing (because of the sparse section bits > > increasing) with CONFIG_X86_PAE=y and CONFIG_X86_PAT=y. This also has to move > > the memory hotplug code from _mapcount to lru.next to avoid any risk of > > clashes. We can't use lru.next for PG_buddy removal, but memory hotplug can use > > lru.next even more easily than the mapcount instead. > > > > Does this make much of a difference? I confess I didn't read the patch closely > because I didn't get the motivation. The motivation is described in the first line. If I wouldn't remove PG_buddy, introducing PG_compound_lock would overflow the 32bit build with CONFIG_X86_PAE=y and CONFIG_X86_PAT=y. The bitflag easier to nuke was PG_buddy. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 1B7896B008A for ; Thu, 9 Dec 2010 13:16:48 -0500 (EST) Date: Thu, 9 Dec 2010 19:15:53 +0100 From: Andrea Arcangeli Subject: Re: [PATCH 45 of 66] remove PG_buddy Message-ID: <20101209181553.GG19131@random.random> References: <85c897773782cdde8b69.1288798100@v2.random> <20101118160801.GA8135@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101118160801.GA8135@csn.ul.ie> Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: linux-mm@kvack.org, Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, Marcelo Tosatti , Adam Litke , Avi Kivity , Hugh Dickins , Rik van Riel , Dave Hansen , Benjamin Herrenschmidt , Ingo Molnar , Mike Travis , KAMEZAWA Hiroyuki , Christoph Lameter , Chris Wright , bpicco@redhat.com, KOSAKI Motohiro , Balbir Singh , "Michael S. Tsirkin" , Peter Zijlstra , Johannes Weiner , Daisuke Nishimura , Chris Mason , Borislav Petkov List-ID: On Thu, Nov 18, 2010 at 04:08:01PM +0000, Mel Gorman wrote: > On Wed, Nov 03, 2010 at 04:28:20PM +0100, Andrea Arcangeli wrote: > > From: Andrea Arcangeli > > > > PG_buddy can be converted to _mapcount == -2. So the PG_compound_lock can be > > added to page->flags without overflowing (because of the sparse section bits > > increasing) with CONFIG_X86_PAE=y and CONFIG_X86_PAT=y. This also has to move > > the memory hotplug code from _mapcount to lru.next to avoid any risk of > > clashes. We can't use lru.next for PG_buddy removal, but memory hotplug can use > > lru.next even more easily than the mapcount instead. > > > > Does this make much of a difference? I confess I didn't read the patch closely > because I didn't get the motivation. The motivation is described in the first line. If I wouldn't remove PG_buddy, introducing PG_compound_lock would overflow the 32bit build with CONFIG_X86_PAE=y and CONFIG_X86_PAT=y. The bitflag easier to nuke was PG_buddy. -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org