Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753617AbXJWJas (ORCPT ); Tue, 23 Oct 2007 05:30:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753253AbXJWJaj (ORCPT ); Tue, 23 Oct 2007 05:30:39 -0400 Received: from one.firstfloor.org ([213.235.205.2]:52845 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753203AbXJWJah (ORCPT ); Tue, 23 Oct 2007 05:30:37 -0400 Date: Tue, 23 Oct 2007 11:30:35 +0200 From: Andi Kleen To: David Chinner Cc: Andi Kleen , Jeremy Fitzhardinge , dean gaudet , Nick Piggin , Xen-devel , Morten@suse.de, Linux Kernel Mailing List , =?iso-8859-1?Q?B=F8geskov?= , xfs@oss.sgi.com, xfs-masters@oss.sgi.com, Mark Williamson Subject: Re: [patch] Re: Interaction between Xen and XFS: stray RW mappings Message-ID: <20071023093035.GB24536@one.firstfloor.org> References: <200710151415.07248.nickpiggin@yahoo.com.au> <471C1A61.1010001@goop.org> <471CEEB4.9040807@goop.org> <20071022190740.GA1695@one.firstfloor.org> <20071022223224.GC995458@sgi.com> <20071022233514.GA9057@one.firstfloor.org> <20071023003641.GF995458@sgi.com> <20071023070414.GM66820511@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071023070414.GM66820511@sgi.com> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2135 Lines: 47 On Tue, Oct 23, 2007 at 05:04:14PM +1000, David Chinner wrote: > On Tue, Oct 23, 2007 at 10:36:41AM +1000, David Chinner wrote: > > On Tue, Oct 23, 2007 at 01:35:14AM +0200, Andi Kleen wrote: > > > On Tue, Oct 23, 2007 at 08:32:25AM +1000, David Chinner wrote: > > > > Could vmap()/vunmap() take references to the pages that are mapped? That > > > > way delaying the unmap would also delay the freeing of the pages and hence > > > > we'd have no problems with the pages being reused before the mapping is > > > > torn down. That'd work for Xen even with XFS's lazy unmapping scheme, and > > > > would allow Nick's more advanced methods to work as well.... > > > > > > You could always just keep around an array of the pages and then drop the > > > reference count after unmap. Or walk the vmalloc mapping and generate such > > > an array before freeing, then unmap and then drop the reference counts. > > > > You mean like vmap() could record the pages passed to it in the area->pages > > array, and we walk and release than in __vunmap() like it already does > > for vfree()? > > > > If we did this, it would probably be best to pass a page release function > > into the vmap or vunmap call - we'd need page_cache_release() called on > > the page rather than __free_page().... > > > > The solution belongs behind the vmap/vunmap interface, not in XFS.... > > Lightly tested(*) patch that does this with lazy unmapping > below for comment. Thanks > > (*) a) kernel boots, b) made an XFS filesystem with 64k directory > blocks, created ~100,000 files in a directory to get a wide btree > (~1700 blocks, still only a single level) and run repeated finds > across it dropping caches in between. Each traversal maps and > unmaps every btree block. Hmm, the __free_page -> page_cache_release() change in vfree() would have been simpler wouldn't it? But if it works it is fine. -Andi - 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/