From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752886AbYAXPnU (ORCPT ); Thu, 24 Jan 2008 10:43:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752570AbYAXPnN (ORCPT ); Thu, 24 Jan 2008 10:43:13 -0500 Received: from host36-195-149-62.serverdedicati.aruba.it ([62.149.195.36]:54118 "EHLO mx.cpushare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752537AbYAXPnN (ORCPT ); Thu, 24 Jan 2008 10:43:13 -0500 Date: Thu, 24 Jan 2008 16:42:39 +0100 From: Andrea Arcangeli To: Christoph Lameter Cc: Robin Holt , Avi Kivity , Izik Eidus , Andrew Morton , Nick Piggin , kvm-devel@lists.sourceforge.net, Benjamin Herrenschmidt , steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, daniel.blueman@quadrics.com, Hugh Dickins Subject: Re: [kvm-devel] [PATCH] export notifier #1 Message-ID: <20080124154239.GP7141@v2.random> References: <4795F9D2.1050503@qumranet.com> <20080122144332.GE7331@v2.random> <20080122200858.GB15848@v2.random> <20080122223139.GD15848@v2.random> <20080123114136.GE15848@v2.random> <20080123123230.GH26420@sgi.com> <20080123173325.GG7141@v2.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 23, 2008 at 12:27:47PM -0800, Christoph Lameter wrote: > There are still dirty bit issues. Yes, but no big issues given ->invalidate_page is fully capable of running set_page_dirty if needed. > > The window that you must close with that bitflag is the request coming > > from the remote node to map the page after the linux pte has been > > cleared. If you map the page in a remote node after the linux pte has > > been cleared ->invalidate_page won't be called again because the page > > will look unmapped in the linux VM. Now invalidate_page will clear the > > bitflag, so the map requests will block. But where exactly you know > > that the linux pte has been cleared so you can "unblock" the map > > requests? If a page is not mapped by some linux pte, mm/rmap.c will > > never be called and this is why any notification in mm/rmap.c should > > track the "address space" and not the "physical page". > > The subsystem needs to establish proper locking for that case. How? I Your answer was to have the subsystem-fault wait PG_exported to return ON... when later you told me the subsystem-fault is the thing supposed to set PG_exported ON again... Perhaps you really could invent a proper locking to make your #v1 workable somehow but I didn't see a sign of it yet. Infact I'm not so sure if all will be race-free with invalidate_page_after (given you pretend to call it outside the PT lock so concurrent linux minor faults can happen in parallel of your invalidate_page_after) but at least it has a better chance to work without having to invent much new complex locking. > It also deals f.e. with page dirty status. I think you should consider if you can also build a rmap per-MM like KVM does and index it by the virtual address like KVM does.