Re: [PATCH] Add a page cache-backed balloon device driver.

[Frank Swiderski <fes@google.com>]

On Tue, Jun 26, 2012 at 2:45 PM, Rik van Riel <riel@redhat.com> wrote:
> On 06/26/2012 05:31 PM, Frank Swiderski wrote:
>>
>> On Tue, Jun 26, 2012 at 1:40 PM, Rik van Riel<riel@redhat.com>  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.
>

Hm, that makes a lot of sense.  That would be a few patches definitely
worth doing, IMHO.  I'm not entirely sure how I feel about inflating
the balloon drivers in the meantime.  Sigh, and I didn't even mean
that as a pun.

fes