Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751532AbXJUWRn (ORCPT ); Sun, 21 Oct 2007 18:17:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750938AbXJUWRg (ORCPT ); Sun, 21 Oct 2007 18:17:36 -0400 Received: from gate.crashing.org ([63.228.1.57]:53649 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750931AbXJUWRf (ORCPT ); Sun, 21 Oct 2007 18:17:35 -0400 Subject: Re: Interaction between Xen and XFS: stray RW mappings From: Benjamin Herrenschmidt Reply-To: benh@kernel.crashing.org To: Andi Kleen Cc: Nick Piggin , David Chinner , Jeremy Fitzhardinge , xfs@oss.sgi.com, Xen-devel , Linux Kernel Mailing List , Mark Williamson , Morten =?ISO-8859-1?Q?B=C3=B8geskov?= , xfs-masters@oss.sgi.com In-Reply-To: <20071015110735.GA11748@one.firstfloor.org> References: <470FA7C3.90404@goop.org> <20071014225618.GN23367404@sgi.com> <200710160056.47458.nickpiggin@yahoo.com.au> <20071015110735.GA11748@one.firstfloor.org> Content-Type: text/plain Date: Mon, 22 Oct 2007 08:16:01 +1000 Message-Id: <1193004961.6745.42.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.12.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1103 Lines: 27 On Mon, 2007-10-15 at 13:07 +0200, Andi Kleen wrote: > On Tue, Oct 16, 2007 at 12:56:46AM +1000, Nick Piggin wrote: > > Is this true even if you don't write through those old mappings? > > I think it happened for reads too. It is a little counter intuitive > because in theory the CPU doesn't need to write back non dirty lines, > but in the one case which took so long to debug exactly this happened > somehow. The problem exist also on ppc, and afaik, is due to the line being in the cache at all (either dirty (write) or not (read)), thus causing the snoop logic to hit, that is what's causing the problem vs. non cached accesses. Also, on some processors, the simple fact of having the page mapped can cause the CPU to prefetch from it even if it's not actually accessed (speculative prefetch can cross page boundaries if things are mapped). Ben. - 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/