From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: [PATCH] Add a page cache-backed balloon device driver. Date: Tue, 26 Jun 2012 17:45:41 -0400 Message-ID: <4FEA2D85.60002@redhat.com> References: <1340742778-11282-1-git-send-email-fes@google.com> <4FEA1E2E.4020806@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Frank Swiderski Cc: Andrea Arcangeli , Rafael Aquini , kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Ying Han , mikew@google.com List-Id: virtualization@lists.linuxfoundation.org On 06/26/2012 05:31 PM, Frank Swiderski wrote: > On Tue, Jun 26, 2012 at 1:40 PM, Rik van Riel wrote: >> The code looks good to me, my only worry is the >> code duplication. We now have 5 balloon drivers, >> for 4 hypervisors, all implementing everything >> from scratch... > > Do you have any recommendations on this? I could (I think reasonably > so) modify the existing virtio_balloon.c and have it change behavior > based on a feature bit or other configuration. I'm not sure that > really addresses the root of what you're pointing out--it's still > adding a different implementation, but doing so as an extension of an > existing one. Ideally, I believe we would have two balloon top parts in a guest (one classical balloon, one on the LRU), and four bottom parts (kvm, xen, vmware & s390). That way the virt specific bits of a balloon driver would be essentially a ->balloon_page and ->release_page callback for pages, as well as methods to communicate with the host. All the management of pages, including stuff like putting them on the LRU, or isolating them for migration, would be done with the same common code, regardless of what virt software we are running on. Of course, that is a substantial amount of work and I feel it would be unreasonable to block anyone's code on that kind of thing (especially considering that your code is good), but I do believe the explosion of balloon code is a little worrying.