From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754686Ab0KIVNV (ORCPT ); Tue, 9 Nov 2010 16:13:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:4373 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752720Ab0KIVNT (ORCPT ); Tue, 9 Nov 2010 16:13:19 -0500 Date: Tue, 9 Nov 2010 22:11:45 +0100 From: Andrea Arcangeli To: KOSAKI Motohiro 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 , Mel Gorman , Dave Hansen , Benjamin Herrenschmidt , Ingo Molnar , Mike Travis , KAMEZAWA Hiroyuki , Christoph Lameter , Chris Wright , bpicco@redhat.com, Balbir Singh , "Michael S. Tsirkin" , Peter Zijlstra , Johannes Weiner , Daisuke Nishimura , Chris Mason , Borislav Petkov Subject: Re: [PATCH 55 of 66] select CONFIG_COMPACTION if TRANSPARENT_HUGEPAGE enabled Message-ID: <20101109211145.GB6809@random.random> References: <89a62752012298bb500c.1288798110@v2.random> <20101109151756.BC7B.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101109151756.BC7B.A69D9226@jp.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 09, 2010 at 03:20:33PM +0900, KOSAKI Motohiro wrote: > > From: Andrea Arcangeli > > > > With transparent hugepage support we need compaction for the "defrag" sysfs > > controls to be effective. > > > > Signed-off-by: Andrea Arcangeli > > --- > > > > diff --git a/mm/Kconfig b/mm/Kconfig > > --- a/mm/Kconfig > > +++ b/mm/Kconfig > > @@ -305,6 +305,7 @@ config NOMMU_INITIAL_TRIM_EXCESS > > config TRANSPARENT_HUGEPAGE > > bool "Transparent Hugepage Support" > > depends on X86 && MMU > > + select COMPACTION > > help > > Transparent Hugepages allows the kernel to use huge pages and > > huge tlb transparently to the applications whenever possible. > > I dislike this. THP and compaction are completely orthogonal. I think > you are talking only your performance recommendation. I mean I dislike > Kconfig 'select' hell and I hope every developers try to avoid it as > far as possible. At the moment THP hangs the system if COMPACTION isn't selected (please try yourself if you don't believe), as without COMPACTION lumpy reclaim wouldn't be entirely disabled. So at the moment it's not orthogonal. When lumpy will be removed from the VM (like I tried multiple times to achieve) I can remove the select COMPACTION in theory, but then 99% of THP users would be still doing a mistake in disabling compaction, even if the mistake won't return in fatal runtime but just slightly degraded performance. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 7C1016B004A for ; Tue, 9 Nov 2010 16:12:52 -0500 (EST) Date: Tue, 9 Nov 2010 22:11:45 +0100 From: Andrea Arcangeli Subject: Re: [PATCH 55 of 66] select CONFIG_COMPACTION if TRANSPARENT_HUGEPAGE enabled Message-ID: <20101109211145.GB6809@random.random> References: <89a62752012298bb500c.1288798110@v2.random> <20101109151756.BC7B.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101109151756.BC7B.A69D9226@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro 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 , Mel Gorman , Dave Hansen , Benjamin Herrenschmidt , Ingo Molnar , Mike Travis , KAMEZAWA Hiroyuki , Christoph Lameter , Chris Wright , bpicco@redhat.com, Balbir Singh , "Michael S. Tsirkin" , Peter Zijlstra , Johannes Weiner , Daisuke Nishimura , Chris Mason , Borislav Petkov List-ID: On Tue, Nov 09, 2010 at 03:20:33PM +0900, KOSAKI Motohiro wrote: > > From: Andrea Arcangeli > > > > With transparent hugepage support we need compaction for the "defrag" sysfs > > controls to be effective. > > > > Signed-off-by: Andrea Arcangeli > > --- > > > > diff --git a/mm/Kconfig b/mm/Kconfig > > --- a/mm/Kconfig > > +++ b/mm/Kconfig > > @@ -305,6 +305,7 @@ config NOMMU_INITIAL_TRIM_EXCESS > > config TRANSPARENT_HUGEPAGE > > bool "Transparent Hugepage Support" > > depends on X86 && MMU > > + select COMPACTION > > help > > Transparent Hugepages allows the kernel to use huge pages and > > huge tlb transparently to the applications whenever possible. > > I dislike this. THP and compaction are completely orthogonal. I think > you are talking only your performance recommendation. I mean I dislike > Kconfig 'select' hell and I hope every developers try to avoid it as > far as possible. At the moment THP hangs the system if COMPACTION isn't selected (please try yourself if you don't believe), as without COMPACTION lumpy reclaim wouldn't be entirely disabled. So at the moment it's not orthogonal. When lumpy will be removed from the VM (like I tried multiple times to achieve) I can remove the select COMPACTION in theory, but then 99% of THP users would be still doing a mistake in disabling compaction, even if the mistake won't return in fatal runtime but just slightly degraded performance. -- 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