From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755365AbXD0GIc (ORCPT ); Fri, 27 Apr 2007 02:08:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755363AbXD0GIc (ORCPT ); Fri, 27 Apr 2007 02:08:32 -0400 Received: from nigel.suspend2.net ([203.171.70.205]:41028 "EHLO nigel.suspend2.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755365AbXD0GIb (ORCPT ); Fri, 27 Apr 2007 02:08:31 -0400 Subject: Re: Back to the future. From: Nigel Cunningham Reply-To: nigel@nigel.suspend2.net To: Pekka J Enberg Cc: Linus Torvalds , LKML In-Reply-To: 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> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-q2bdYnfD/WIxBrNHe7xq" Date: Fri, 27 Apr 2007 16:08:30 +1000 Message-Id: <1177654110.4737.91.camel@nigel.suspend2.net> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --=-q2bdYnfD/WIxBrNHe7xq Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Hi. On Fri, 2007-04-27 at 07:52 +0300, 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=20 > > > (and if you want to support snapshots > 4GB, be my guest, but I su= spect=20 > > > you're actually *better* off just admitting that if you cannot shr= ink=20 > > > the snapshot to less than 32 bits, it's not worth doing) > =20 > 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. >=20 > It doesn't. We can make the userspace mapped pages copy-on-write. As long= =20 > as the userspace makes sure there's not much activity during=20 > snapshot/shutdown, we will be fine. What we probably do need to copy is=20 > kernel pages. 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? I was going to leave it at that and press send, but perhaps that wouldn't be wise. I feel I should also ask what you're thinking of as a means of making sure userspace doesn't do much activity. Thanks for your labours! Regards, Nigel --=-q2bdYnfD/WIxBrNHe7xq Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQBGMZNeN0y+n1M3mo0RAopDAJ4nqnszwtQlbMllFX8JVksRge9qbgCgmilK phxPNqXDVHepzuCrVm2DuNU= =0GSP -----END PGP SIGNATURE----- --=-q2bdYnfD/WIxBrNHe7xq--