linux-kernel - Re: [PATCH v7 2/4] virtio_balloon: introduce migration primitives to balloon pages

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Message-ID: <20120814213832.GA29180@redhat.com>
Date:	Wed, 15 Aug 2012 00:38:32 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Rafael Aquini <aquini@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mel Gorman <mel@....ul.ie>, Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH v7 2/4] virtio_balloon: introduce migration primitives to
 balloon pages

On Tue, Aug 14, 2012 at 04:56:59PM -0400, Rik van Riel wrote:
> On 08/14/2012 04:54 PM, Michael S. Tsirkin wrote:
> 
> >To clarify, the global state that this patch adds, is ugly
> >even if we didn't support multiple balloons yet.
> >So I don't think I can accept such a patch.
> >Rusty has a final word here, maybe he thinks differently.
> 
> Before deciding that "does not support multiple balloon drivers
> at once" is an issue, is there any use case at all for having
> multiple balloon drivers active at a time?
> 
> I do not see any.

For example, we had a proposal for a page-cache backed
device. So it could be useful to have two, a regular balloon
and a pagecache backed one.
There could be other uses - it certainly looks like it
works so how can you be sure it's useless?

And even ignoring that, global pointer to a device
is an ugly hack and ugly hacks tend to explode.

And even ignoring estetics, and if we decide we are fine
with a single balloon, it needs to fail gracefully not
crash like it does now.

> -- 
> All rights reversed
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