From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: Question on Lazy VM Restore Date: Sat, 14 Dec 2013 16:28:29 +0000 Message-ID: <52AC872D.3080702@citrix.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Prateek Sharma , xen-devel@lists.xen.org Cc: Andres Lagar-Cavilla List-Id: xen-devel@lists.xenproject.org On 13/12/2013 16:06, Prateek Sharma wrote: > Hello all, > I was wondering if there is an existing mechanism in Xen for > restoring a saved/checkpointed VM lazily. By that, I mean that the > pages of the VM should be mapped only on access. > Currently, restoring a VM from a snapshot seems to take a long > time [~20 seconds for 2 GB]. > Assuming that there is no lazy-restore functionality, what would > be a good way to implement this? Using parts of Xen-paging? Snowflock? > Something else? > > Thanks! > --Prateek There is no current mechanism which I am aware of. I recall a few academic papers looking in to the possibility, but no code as a result. The restoring from a shapshot has a number of large inefficiencies in the datapath in the privcmd driver. Fixing these would make quite an improvement on those 20 seconds, which I suspect might be a rather easier improvement than implementing lazy restore. Having said that, if you are looking for a project to do, I suspect the xen-paging infrastructure would be able to be used for lazy restore, although Andres (author of xen-paging, CC'd) will likely be able to speak rather more about the feasibility of it. ~Andrew