Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752673Ab0DXKwt (ORCPT ); Sat, 24 Apr 2010 06:52:49 -0400 Received: from gir.skynet.ie ([193.1.99.77]:48544 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752186Ab0DXKwr (ORCPT ); Sat, 24 Apr 2010 06:52:47 -0400 Date: Sat, 24 Apr 2010 11:52:27 +0100 From: Mel Gorman To: Andrea Arcangeli Cc: Minchan Kim , KAMEZAWA Hiroyuki , Christoph Lameter , Andrew Morton , Adam Litke , Avi Kivity , David Rientjes , KOSAKI Motohiro , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache pages Message-ID: <20100424105226.GF14351@csn.ul.ie> References: <20100422193106.9ffad4ec.kamezawa.hiroyu@jp.fujitsu.com> <20100422195153.d91c1c9e.kamezawa.hiroyu@jp.fujitsu.com> <1271946226.2100.211.camel@barrios-desktop> <1271947206.2100.216.camel@barrios-desktop> <20100422154443.GD30306@csn.ul.ie> <20100423183135.GT32034@random.random> <20100423192311.GC14351@csn.ul.ie> <20100423193948.GU32034@random.random> <20100423213549.GV32034@random.random> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100423213549.GV32034@random.random> 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 Content-Length: 2740 Lines: 60 On Fri, Apr 23, 2010 at 11:35:49PM +0200, Andrea Arcangeli wrote: > On Fri, Apr 23, 2010 at 09:39:48PM +0200, Andrea Arcangeli wrote: > > On Fri, Apr 23, 2010 at 08:23:12PM +0100, Mel Gorman wrote: > > > On Fri, Apr 23, 2010 at 08:31:35PM +0200, Andrea Arcangeli wrote: > > > > Hi Mel, > > > > > > > > On Thu, Apr 22, 2010 at 04:44:43PM +0100, Mel Gorman wrote: > > > > > heh, I thought of a similar approach at the same time as you but missed > > > > > this mail until later. However, with this approach I suspect there is a > > > > > possibility that two walkers of the same anon_vma list could livelock if > > > > > two locks on the list are held at the same time. Am still thinking of > > > > > how it could be resolved without introducing new locking. > > > > > > > > Trying to understand this issue and I've some questions. This > > > > vma_adjust and lock inversion troubles with the anon-vma lock in > > > > rmap_walk are a new issue introduced by the recent anon-vma changes, > > > > right? > > > > > > > > > > In a manner of speaking. There was no locking going on but prior to the > > > anon_vma changes, there would have been only one anon_vma lock and the > > > fix would be easier - just take the lock on anon_vma->lock while the > > > VMAs are being updated. > > > > So it was very much a bug before too and we could miss to find some > > pte mapping the page if vm_start was adjusted? > > Well I looked deeper into it myself as I wanted to have this bit (and > other bits) sorted out in aa.git, and definitely this is a bug > introduced by the newest anon-vma changes in 2.6.34-rc so aa.git > cannot be affected as it's using the 2.6.33 anon-vma (and prev) code. > I think you're right. This is a new bug introduced by the anon_vma changes. On the plus side, it means we don't have to worry about -stable. > vma_adjust already takes the anon_vma->lock and of course I also > further verified that trying to apply your snippet to vma_adjust > results in immediately deadlock as the very same lock is already taken > in my tree as it's the same anon-vma (simpler). Yes, I expected that. Previously, there was only one anon_vma so if you double-take the lock, bad things happen. > So aa.git will be > immune from these bugs for now. > It should be. I expect that's why you have never seen the bugon in swapops. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/