Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754783AbYJ3Lr7 (ORCPT ); Thu, 30 Oct 2008 07:47:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753386AbYJ3Lru (ORCPT ); Thu, 30 Oct 2008 07:47:50 -0400 Received: from bohort.kerlabs.com ([62.160.40.57]:40608 "EHLO bohort.kerlabs.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753081AbYJ3Lru (ORCPT ); Thu, 30 Oct 2008 07:47:50 -0400 Date: Thu, 30 Oct 2008 12:47:47 +0100 From: Louis Rilling To: Andrey Mirkin Cc: Oren Laadan , Dave Hansen , "Serge E. Hallyn" , Cedric Le Goater , Daniel Lezcano , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [Devel] Re: [PATCH 0/9] OpenVZ kernel based checkpointing/restart Message-ID: <20081030114747.GL15171@hawkmoon.kerlabs.com> Reply-To: Louis.Rilling@kerlabs.com References: <1220439476-16465-1-git-send-email-major@openvz.org> <200810271707.13580.major@openvz.org> <4905D2AD.1070309@cs.columbia.edu> <200810300902.47067.major@openvz.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=_bohort-30093-1225367121-0001-2" Content-Disposition: inline In-Reply-To: <200810300902.47067.major@openvz.org> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3270 Lines: 85 This is a MIME-formatted message. If you see this text it means that your E-mail software does not support MIME-formatted messages. --=_bohort-30093-1225367121-0001-2 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Oct 30, 2008 at 10:02:44AM +0400, Andrey Mirkin wrote: > > > kernel. Also we will need a functionolity to create processes with > > > predefined PID. I think it is not very good to provide such ability to > > > user space. That is why we prefer in OpenVZ to do all the job in kern= el. > > > > This is the weak side of creating the processes in user space - > > that we need such an interface. Note, however, that we can > > easily "hide" it inside the interface of the sys_restart() call, > > and restrict how it may be used. >=20 > Of course we can "hide" it somehow, but anyway we will have a hole and th= at is=20 > not good. >=20 > Anyway we should ask everyone what they think about user- and kernel- bas= ed=20 > process creation. > Dave, Serge, Cedric, Daniel, Louis what do you think about that? Frankly, I'm not convinced (yet) that one approach is better than the other= one. I only *tend* to prefer kernel-based, for the reasons explained below. I kn= ow that there are arguments in favor of userspace (I've at least seen security-related ones), but I let their authors detail them (again). In Kerrighed this is kernel-based, and will remain kernel-based because we checkpoint a distributed task tree, and want to restart it as mush as possi= ble with the same distribution. The distributed protocol used for restart is currently too fragile and complex to rely on customized user-space implementations. That said, if someone brings very good arguments in favor = of userspace implementations, we might consider changing this. Without taking distributed restart into account, I also tend to prefer kernel-based, mainly for two (not so strong) reasons: 1) this prevents userspace from doing weird things, like changing the task = tree and let the kernel detect it and deal with the mess this creates (think abo= ut two threads being restarted in separate processes that do not even share th= eir parents). But one can argue that userspace can change the checkpoint image = as well, so that the kernel must check for such weird things anyway. 2) restart will be more efficient with respect to shared objects. Louis --=20 Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes --=_bohort-30093-1225367121-0001-2 Content-Type: application/pgp-signature; name="signature.asc" Content-Transfer-Encoding: 7bit Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFJCZ7jVKcRuvQ9Q1QRApKeAKCsUFFiC/RJBW7wNKKF7iPjAms5sACdG9cr b9+Zh+eBenOil48XhDZU3ws= =a0Rz -----END PGP SIGNATURE----- --=_bohort-30093-1225367121-0001-2-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/