From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760660AbZENMCy (ORCPT ); Thu, 14 May 2009 08:02:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760721AbZENMCf (ORCPT ); Thu, 14 May 2009 08:02:35 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:50127 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761145AbZENMCe (ORCPT ); Thu, 14 May 2009 08:02:34 -0400 From: KOSAKI Motohiro To: Robin Holt Subject: Re: [PATCH 4/4] zone_reclaim_mode is always 0 by default Cc: kosaki.motohiro@jp.fujitsu.com, Rik van Riel , LKML , linux-mm , Andrew Morton , Christoph Lameter In-Reply-To: <20090514114827.GN7601@sgi.com> References: <20090514170721.9B75.A69D9226@jp.fujitsu.com> <20090514114827.GN7601@sgi.com> Message-Id: <20090514205654.9B8A.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Thu, 14 May 2009 21:02:32 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > Unfortunately no. > > zone reclaim has two weakness by design. > > > > 1. > > zone reclaim don't works well when workingset size > local node size. > > but it can happen easily on small machine. > > if it happen, zone reclaim drop own process's memory. > > > > Plus, zone reclaim also doesn't fit DB server. its process has large > > workingset. > > Large DB server is not your typical desktop application either. ack. > > 2. > > zone reclaim have inter zone balancing issue. > > > > example: x86_64 2node 8G machine has following zone assignment > > > > zone 0 (DMA32): 3GB > > zone 0 (Normal): 1GB > > zone 1 (Normal): 4GB > > > > if the page is allocated from DMA32, you are lucky. DMA32 isn't reclaimed > > so freqently. but if from zone0 Normal, you are unlucky. > > it is very frequent reclaimed although it is small than other zone. > > I have seen that behavior on some of our mismatched large systems as well, > although never had one so imbalanced because ia64 only has Normal. not true. some ia64 server has about 2GB DMA zone. SGI ia64 is special one. > > I know my patch change large server default. but I believe linux > > default kernel parameter adapt to desktop and entry machine. > > If this imbalance is an x86_64 only problem, then we could do something > simple like the following untested patch. This leaves the default > for everyone except x86_64. not x86_64 only. many 64bit architecture have 2 or 4GB DMA zone. even though, your patch seems interesting. at least it solve desktop user issue and we don't need to care another area user. embedded and high-end server user is typically skillfull. they can change kernel parameter by themself. > > Robin > > ------------------------------------------------------------------------ > > Even if there is a great node distance on x86_64, disable zone reclaim > by default. This was done to handle the imbalanced zone sizes where a > majority of the memory in zone 0 is DMA32 with a small remaining Normal > which will be aggressively reclaimed. > > For other architectures, we leave the default behavior. > > Signed-off-by: Robin Holt > Cc: KOSAKI Motohiro > Cc: Christoph Lameter > Cc: Rik van Riel > > --- > arch/x86/include/asm/topology.h | 2 ++ > include/linux/topology.h | 5 +++++ > mm/page_alloc.c | 2 +- > 3 files changed, 8 insertions(+), 1 deletion(-) > Index: page_reclaim_mode/arch/x86/include/asm/topology.h > =================================================================== > --- page_reclaim_mode.orig/arch/x86/include/asm/topology.h 2009-05-14 06:44:20.118925713 -0500 > +++ page_reclaim_mode/arch/x86/include/asm/topology.h 2009-05-14 06:44:21.251067716 -0500 > @@ -128,6 +128,8 @@ extern unsigned long node_remap_size[]; > > #endif > > +#define DEFAULT_ZONE_RECLAIM_MODE 0 > + > /* sched_domains SD_NODE_INIT for NUMA machines */ > #define SD_NODE_INIT (struct sched_domain) { \ > .min_interval = 8, \ > Index: page_reclaim_mode/include/linux/topology.h > =================================================================== > --- page_reclaim_mode.orig/include/linux/topology.h 2009-05-14 06:44:20.070919619 -0500 > +++ page_reclaim_mode/include/linux/topology.h 2009-05-14 06:44:21.279071382 -0500 > @@ -61,6 +61,11 @@ int arch_update_cpu_topology(void); > */ > #define RECLAIM_DISTANCE 20 > #endif > + > +#ifndef DEFAULT_ZONE_RECLAIM_MODE > +#define DEFAULT_ZONE_RECLAIM_MODE 1 > +#endif > + > #ifndef PENALTY_FOR_NODE_WITH_CPUS > #define PENALTY_FOR_NODE_WITH_CPUS (1) > #endif > Index: page_reclaim_mode/mm/page_alloc.c > =================================================================== > --- page_reclaim_mode.orig/mm/page_alloc.c 2009-05-14 06:44:20.138928363 -0500 > +++ page_reclaim_mode/mm/page_alloc.c 2009-05-14 06:44:21.311075244 -0500 > @@ -2331,7 +2331,7 @@ static void build_zonelists(pg_data_t *p > * to reclaim pages in a zone before going off node. > */ > if (distance > RECLAIM_DISTANCE) > - zone_reclaim_mode = 1; > + zone_reclaim_mode = DEFAULT_ZONE_RECLAIM_MODE; > > /* > * We don't want to pressure a particular node.