From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757333AbXD0VZx (ORCPT ); Fri, 27 Apr 2007 17:25:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757332AbXD0VZx (ORCPT ); Fri, 27 Apr 2007 17:25:53 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:58670 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757333AbXD0VZh (ORCPT ); Fri, 27 Apr 2007 17:25:37 -0400 From: "Rafael J. Wysocki" To: Pekka J Enberg Subject: Re: Back to the future. Date: Fri, 27 Apr 2007 22:44:07 +0200 User-Agent: KMail/1.9.5 Cc: Nigel Cunningham , Linus Torvalds , LKML References: <1177567481.5025.211.camel@nigel.suspend2.net> <1177617379.4737.29.camel@nigel.suspend2.net> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200704272244.08102.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Friday, 27 April 2007 06:52, Pekka J Enberg wrote: > On Thu, 2007-04-26 at 09:56 -0700, Linus Torvalds wrote: > > > which will map in the snapshot, return the mapped address and the size > > > (and if you want to support snapshots > 4GB, be my guest, but I suspect > > > you're actually *better* off just admitting that if you cannot shrink > > > the snapshot to less than 32 bits, it's not worth doing) > > On Fri, 27 Apr 2007, Nigel Cunningham wrote: > > That inherently limits the image to half of available ram (you need > > somewhere to store the snapshot), so you won't get the full image you > > express interest in below. > > It doesn't. We can make the userspace mapped pages copy-on-write. As long > as the userspace makes sure there's not much activity during > snapshot/shutdown, we will be fine. What we probably do need to copy is > kernel pages. The user space is (and IMHO should be) frozen way before that and what you're suggesting here is what I wanted to implement some time ago. The problem with this was that the user space pages may be updated, for example, by device drivers as a result of some deferred I/O after we've snapshotted the system. I didn't know how to find out which pages owned by the user space could be updated this way, so I gave up at that time. Greetings, Rafael