Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758518AbYCNVjU (ORCPT ); Fri, 14 Mar 2008 17:39:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754774AbYCNVjL (ORCPT ); Fri, 14 Mar 2008 17:39:11 -0400 Received: from gw.goop.org ([64.81.55.164]:45664 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754730AbYCNVjK (ORCPT ); Fri, 14 Mar 2008 17:39:10 -0400 Message-ID: <47DAF000.1010802@goop.org> Date: Fri, 14 Mar 2008 14:37:04 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: Zachary Amsden CC: Hugh Dickins , Martin Schwidefsky , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, virtualization@lists.osdl.org, akpm@linux-foundation.org, nickpiggin@yahoo.com.au, frankeh@watson.ibm.com, rusty@rustcorp.com.au, andrea@qumranet.com, clameter@sgi.com, a.p.zijlstra@chello.nl, Keir Fraser , Ian Pratt Subject: Re: [patch 0/6] Guest page hinting version 6. References: <20080312132132.520833247@de.ibm.com> <47D9754B.1030509@goop.org> <1205438038.14987.1.camel@bodhitayantram.eng.vmware.com> <47DAC435.1050105@goop.org> <1205530358.14987.32.camel@bodhitayantram.eng.vmware.com> In-Reply-To: <1205530358.14987.32.camel@bodhitayantram.eng.vmware.com> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1648 Lines: 34 Zachary Amsden wrote: > It needn't be that hard on s390, I believe you don't need to worry about > PTEs becoming asynchronous when stealing a page, since if I understand > the hypervisor architecture, there is a per-page mapping level > available, allowing you to generate discard faults on access. It might > be possible to use this mapping layer without implementing a full blown > hypervisor. Martin? > Yes, I don't expect its a problem for s390, but the point is making something workalike enough to make sure there's an evenly distributed number of explosions-in-face when things go wrong. > For x86, at discard time, you would have to manually walk and invalidate > any PTEs potentially mapping the discarded page, but there is already > this great thing called Xen paravirt-ops which actually does that for > completely different reasons (PT page protection). > Not sure I follow. Xen pvops pays attention to whether a particular page is being used as part of a pagetable, and changes its permissions accordingly. But because pagetable pages are strictly kernel-only, we can get away with updating a single kernel-mapping pte which is shared across all processes. In the guest page hinting case, we need to deal with general pages which can be mapped anywhere, so that really does require a full traversal of the pagetables. Presumably rmap would be helpful here. 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/