From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id 907726B004D for ; Thu, 12 Mar 2009 00:14:26 -0400 (EDT) Received: from d28relay02.in.ibm.com (d28relay02.in.ibm.com [9.184.220.59]) by e28smtp03.in.ibm.com (8.13.1/8.13.1) with ESMTP id n2C4EJmv002183 for ; Thu, 12 Mar 2009 09:44:19 +0530 Received: from d28av01.in.ibm.com (d28av01.in.ibm.com [9.184.220.63]) by d28relay02.in.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n2C4B8tB1925310 for ; Thu, 12 Mar 2009 09:41:08 +0530 Received: from d28av01.in.ibm.com (loopback [127.0.0.1]) by d28av01.in.ibm.com (8.13.1/8.13.3) with ESMTP id n2C4EJpZ030784 for ; Thu, 12 Mar 2009 09:44:19 +0530 Date: Thu, 12 Mar 2009 09:44:14 +0530 From: Balbir Singh Subject: Re: [BUGFIX][PATCH 1/5] memcg use correct scan number at reclaim Message-ID: <20090312041414.GG23583@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090312095247.bf338fe8.kamezawa.hiroyu@jp.fujitsu.com> <20090312095516.53a2d029.kamezawa.hiroyu@jp.fujitsu.com> <20090312034918.GB23583@balbir.in.ibm.com> <20090312125124.06af6ad9.kamezawa.hiroyu@jp.fujitsu.com> <20090312040054.GE23583@balbir.in.ibm.com> <20090312130556.68d03711.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20090312130556.68d03711.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "nishimura@mxp.nes.nec.co.jp" , "kosaki.motohiro@jp.fujitsu.com" , "akpm@linux-foundation.org" List-ID: * KAMEZAWA Hiroyuki [2009-03-12 13:05:56]: > On Thu, 12 Mar 2009 09:30:54 +0530 > Balbir Singh wrote: > > > * KAMEZAWA Hiroyuki [2009-03-12 12:51:24]: > > > > > On Thu, 12 Mar 2009 09:19:18 +0530 > > > Balbir Singh wrote: > > > > > > > * KAMEZAWA Hiroyuki [2009-03-12 09:55:16]: > > > > > > > > > Andrew, this [1/5] is a bug fix, others are not. > > > > > > > > > > == > > > > > From: KOSAKI Motohiro > > > > > > > > > > Even when page reclaim is under mem_cgroup, # of scan page is determined by > > > > > status of global LRU. Fix that. > > > > > > > > > > Signed-off-by: KOSAKI Motohiro > > > > > Signed-off-by: KAMEZAWA Hiroyuki > > > > > --- > > > > > mm/vmscan.c | 2 +- > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > Index: mmotm-2.6.29-Mar10/mm/vmscan.c > > > > > =================================================================== > > > > > --- mmotm-2.6.29-Mar10.orig/mm/vmscan.c > > > > > +++ mmotm-2.6.29-Mar10/mm/vmscan.c > > > > > @@ -1470,7 +1470,7 @@ static void shrink_zone(int priority, st > > > > > int file = is_file_lru(l); > > > > > int scan; > > > > > > > > > > - scan = zone_page_state(zone, NR_LRU_BASE + l); > > > > > + scan = zone_nr_pages(zone, sc, l); > > > > > > > > I have the exact same patch in my patch queue. BTW, mem_cgroup_zone_nr_pages is > > > > buggy. We don't hold any sort of lock while extracting > > > > MEM_CGROUP_ZSTAT (ideally we need zone->lru_lock). Without that how do > > > > we guarantee that MEM_CGRUP_ZSTAT is not changing at the same time as > > > > we are reading it? > > > > > > > Is it big problem ? We don't need very precise value and ZSTAT just have > > > increment/decrement. So, I tend to ignore this small race. > > > (and it's unsigned long, not long long.) > > > > > > > The assumption is that unsigned long read is atomic even on 32 bit > > systems? What if we get pre-empted in the middle of reading the data > > and don't return back for long? The data can be highly in-accurate. > > No? > > > Hmm, preempt_disable() is appropriate ? > > But shrink_zone() itself works on the value which is read at this time and > dont' take care of changes in situation by preeemption...so it's not problem > of memcg. > You'll end up reclaiming based on old stale data. shrink_zone itself maintains atomic data for zones. I think the assumption that unsigned long read is atomic seems quite reasonable, but I want to validate this across architectures. Anyone know the correct answer? -- Balbir -- 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