From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Daniel P. Berrange" Subject: Re: [PATCH 1/2] PV hugepages - Xen patch Date: Thu, 9 Oct 2008 09:38:48 +0100 Message-ID: <20081009083848.GB26108@redhat.com> References: <48ED3950.1080605@goop.org> Reply-To: "Daniel P. Berrange" Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <48ED3950.1080605@goop.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jeremy Fitzhardinge Cc: xen-devel@lists.xensource.com, Ian Pratt , Dave McCracken , Keir Fraser List-Id: xen-devel@lists.xenproject.org On Wed, Oct 08, 2008 at 03:50:56PM -0700, Jeremy Fitzhardinge wrote: > Keir Fraser wrote: > >Actually this is an interesting one. For a PV guest it may be in general > >unsolvable, since the target machine may not have allocatable 2MB extents. > >It may also screw live migration since 2MB is a very coarse granularity to > >do dirty-page tracking. One option: perhaps the PV kernel could shatter and > >then reconstruct (as best it can) superpage mappings across save/restore? > > That means you need to notify the guest when you're starting a live > migration, rather than just springing it on them at the last moment as > we do now. > > But shattering large pages all over the place is going to be pretty > expensive, and possibly awkward if it suddenly needs to come up with a > pile of pages for the new L1 entries. Or you could just take the view this is a pre-migration capability check, and that admin (or mgmt app) must ensure sufficient free hugepages on the destination before attempting migration. If this isn't satisfied then XenD can just fail / abort the migration op and leave it running on original host. Dainel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|