From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932691AbWF0I61 (ORCPT ); Tue, 27 Jun 2006 04:58:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932806AbWF0I61 (ORCPT ); Tue, 27 Jun 2006 04:58:27 -0400 Received: from pop5-1.us4.outblaze.com ([205.158.62.125]:53194 "HELO pop5-1.us4.outblaze.com") by vger.kernel.org with SMTP id S932691AbWF0I6Z (ORCPT ); Tue, 27 Jun 2006 04:58:25 -0400 From: Nigel Cunningham Reply-To: nigel@suspend2.net To: Greg KH Subject: Re: [Suspend2][ 0/9] Extents support. Date: Tue, 27 Jun 2006 18:58:17 +1000 User-Agent: KMail/1.9.1 Cc: Jens Axboe , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org References: <20060626165404.11065.91833.stgit@nigel.suspend2.net> <20060627075906.GK22071@suse.de> <20060627081252.GC7181@kroah.com> In-Reply-To: <20060627081252.GC7181@kroah.com> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart9376943.bcYqeLmXqz"; protocol="application/pgp-signature"; micalg=pgp-sha1 Content-Transfer-Encoding: 7bit Message-Id: <200606271858.21810.nigel@suspend2.net> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --nextPart9376943.bcYqeLmXqz Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Hi. On Tuesday 27 June 2006 18:12, Greg KH wrote: > On Tue, Jun 27, 2006 at 09:59:06AM +0200, Jens Axboe wrote: > > Now I haven't followed the suspend2 vs swsusp debate very closely, but > > it seems to me that your biggest problem with getting this merged is > > getting consensus on where exactly this is going. Nobody wants two > > different suspend modules in the kernel. So there are two options - > > suspend2 is deemed the way to go, and it gets merged and replaces > > swsusp. Or the other way around - people like swsusp more, and you are > > doomed to maintain suspend2 outside the tree. > > Actually, there's a third option that is looking like the way forward, > doing all of this from userspace and having no suspend-to-disk in the > kernel tree at all. > > Pavel and others have a working implementation and are slowly moving > toward adding all of the "bright and shiny" features that is in suspend2 > to it (encryption, progress screens, abort by pressing a key, etc.) so > that there is no loss of functionality. > > So I don't really see the future of suspend2 because of this... But what Rafael and Pavel are doing is really only moving the highest level= of=20 controlling logic to userspace (ok, and maybe compression and encryption=20 too). Everything important (freezing other processes, atomic copy and the=20 guts of the I/O) is still done by the kernel. And there _is_ loss of functionality - uswsusp still doesn't support writin= g a=20 full image of memory, writing to multiple swap devices (partitions or files= ),=20 or writing to ordinary files. They're getting the low hanging fruit, but wh= en=20 it comes to these parts of the problem, they're going to require either smo= ke=20 and very good mirrors (eg the swap prefetching trick), or simply refuse to= =20 implement them. If we take the problem one step further, and begin to think about=20 checkpointing, they're in even bigger trouble. I'll freely admit that I'd=20 have to redesign the way I store data so that random parts of the image cou= ld=20 be replaced, have hooks in mm to be able to learn what pages need have=20 changed and would also need filesystem support to handle that part of the=20 problem, but I'd at least be working in the right domain. I don't want to demean Rafael and Pavels' work for a moment. I've benefited= =20 from Pavel's help of Gabor in the beginning, and a little bit since he fork= ed=20 and merged in 2.5. But it seems to me that uswsusp is a short trip down a=20 dead end road. It just doesn't have a future beyond being an interesting ha= ck=20 that proves you can safely run a program in userspace while snapshotting.=20 Suspending to disk belongs in the kernel. That is shown clearly by the fact= =20 that uswsusp continues to use kernel code to do the really critical tasks,= =20 rather than being some super privileged userspace program that does them=20 itself from userspace. Regards, Nigel =2D-=20 See http://www.suspend2.net for Howtos, FAQs, mailing lists, wiki and bugzilla info. --nextPart9376943.bcYqeLmXqz Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (GNU/Linux) iD8DBQBEoPMtN0y+n1M3mo0RAordAKC4+0OGANEebwo8KdDVmELFlldQzgCg5NCQ 9z0klf2zBhltVF9CnBGL4Tc= =LzWm -----END PGP SIGNATURE----- --nextPart9376943.bcYqeLmXqz--