Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763538AbXJNXMa (ORCPT ); Sun, 14 Oct 2007 19:12:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752902AbXJNXMW (ORCPT ); Sun, 14 Oct 2007 19:12:22 -0400 Received: from gw.goop.org ([64.81.55.164]:36652 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751343AbXJNXMW (ORCPT ); Sun, 14 Oct 2007 19:12:22 -0400 Message-ID: <4712A254.4090604@goop.org> Date: Sun, 14 Oct 2007 16:12:20 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.5 (X11/20070727) MIME-Version: 1.0 To: David Chinner CC: xfs@oss.sgi.com, Xen-devel , Linux Kernel Mailing List , Mark Williamson , =?ISO-8859-1?Q?Morten_?= =?ISO-8859-1?Q?B=F8geskov?= , xfs-masters@oss.sgi.com, nickpiggin@yahoo.com.au Subject: Re: Interaction between Xen and XFS: stray RW mappings References: <470FA7C3.90404@goop.org> <20071014225618.GN23367404@sgi.com> In-Reply-To: <20071014225618.GN23367404@sgi.com> X-Enigmail-Version: 0.95.3 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1303 Lines: 36 David Chinner wrote: > You mean xfs_buf.c. > Yes, sorry. > And yes, we delay unmapping pages until we have a batch of them > to unmap. vmap and vunmap do not scale, so this is batching helps > alleviate some of the worst of the problems. > How much performance does it cost? What kind of workloads would it show up under? > Realistically, if this delayed release of vmaps is a problem for > Xen, then I think that some generic VM solution is needed to this > problem as vmap() is likely to become more common in future (think > large blocks in filesystems). Nick - any comments? > Well, the only real problem is that the pages are returned to the free pool and reallocated while still being part of a mapping. If the pages are still owned by the filesystem/pagecache, then there's no problem. What's the lifetime of things being vmapped/unmapped in xfs? Are they necessarily being freed when they're unmapped, or could unmapping of freed memory be more immediate than other memory? Maybe it just needs a notifier chain or something. J - 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/