From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755377AbXD0G3N (ORCPT ); Fri, 27 Apr 2007 02:29:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755369AbXD0G3M (ORCPT ); Fri, 27 Apr 2007 02:29:12 -0400 Received: from courier.cs.helsinki.fi ([128.214.9.1]:54191 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755379AbXD0G3M (ORCPT ); Fri, 27 Apr 2007 02:29:12 -0400 Date: Fri, 27 Apr 2007 09:29:10 +0300 (EEST) From: Pekka J Enberg To: Nigel Cunningham cc: Linus Torvalds , LKML Subject: Re: Back to the future. In-Reply-To: Message-ID: References: <1177567481.5025.211.camel@nigel.suspend2.net> <84144f020704260028q190fc90fs8f9ea703e42e7910@mail.gmail.com> <1177573348.5025.224.camel@nigel.suspend2.net> <1177617379.4737.29.camel@nigel.suspend2.net> <1177654110.4737.91.camel@nigel.suspend2.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 27 Apr 2007, Nigel Cunningham wrote: > > COW is a possibility, but I understood (perhaps wrongly) that Linus was > > thinking of a single syscall or such like to prepare the snapshot. If > > you're going to start doing things like this, won't that mean you'd then > > have to update/redo the snapshot or somehow nullify the effect of > > anything the programs does so that doing it again after the snapshot is > > restored doesn't cause problems? On Fri, 27 Apr 2007, Pekka J Enberg wrote: > No. The snapshot is just that. A snapshot in time. From kernel point of > view, it doesn't matter one bit what when you did it or if the state has > changed before you resume. It's up to userspace to make sure the user > doesn't do real work while the snapshot is being written to disk and > machine is shut down. Btw, obviously we need to break the COW when resuming and not include the snapshot mapping. However, that should be trivially doable by snapshotting the page mappings before remapping them as COW. Pekka