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

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Message-ID: <CAK+C7kVHeUz7nUV1vtSHrK6vXorLsZoos82NFm0P0Ux0rEOZGQ@mail.gmail.com>
Date:	Tue, 26 Jun 2012 16:45:36 -0700
From:	Frank Swiderski <fes@...gle.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	mikew@...gle.com, Ying Han <yinghan@...gle.com>,
	Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH] Add a page cache-backed balloon device driver.

On Tue, Jun 26, 2012 at 2:45 PM, Rik van Riel <riel@...hat.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@...hat.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
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