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

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Message-ID: <87lij91myw.fsf@rustcorp.com.au>
Date:	Wed, 27 Jun 2012 12:26:55 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	Frank Swiderski <fes@...gle.com>
Cc:	riel@...hat.com, Andrea Arcangeli <aarcange@...hat.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mikew@...gle.com
Subject: Re: [PATCH] Add a page cache-backed balloon device driver.

On Wed, 27 Jun 2012 00:41:06 +0300, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Tue, Jun 26, 2012 at 01:32:58PM -0700, Frank Swiderski wrote:
> > This implementation of a virtio balloon driver uses the page cache to
> > "store" pages that have been released to the host.  The communication
> > (outside of target counts) is one way--the guest notifies the host when
> > it adds a page to the page cache, allowing the host to madvise(2) with
> > MADV_DONTNEED.  Reclaim in the guest is therefore automatic and implicit
> > (via the regular page reclaim).  This means that inflating the balloon
> > is similar to the existing balloon mechanism, but the deflate is
> > different--it re-uses existing Linux kernel functionality to
> > automatically reclaim.
> > 
> > Signed-off-by: Frank Swiderski <fes@...gle.com>
> 
> I'm pondering this:
> 
> Should it really be a separate driver/device ID?
> If it behaves the same from host POV, maybe it
> should be up to the guest how to inflate/deflate
> the balloon internally?

Well, it shouldn't steal ID 10, either way :)  Either use a completely
bogus number, or ask for an id.

But AFAICT this should be a an alternate driver of for the same device:
it's not really a separate device, is it?

Cheers,
Rusty.
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