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

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Message-ID: <20120814203123.GC28990@redhat.com>
Date:	Tue, 14 Aug 2012 23:31:23 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Rik van Riel <riel@...hat.com>, 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 05:11:13PM -0300, Rafael Aquini wrote:
> On Tue, Aug 14, 2012 at 10:51:39PM +0300, Michael S. Tsirkin wrote:
> > What I think you should do is use rcu for access.
> > And here sync rcu before freeing.
> > Maybe an overkill but at least a documented synchronization
> > primitive, and it is very light weight.
> > 
> 
> I liked your suggestion on barriers, as well.
> 
> Rik, Mel ?

Further instead of simple assignment I would add an api
in mm to set/clear the balloon mapping, with proper locking.

This could fail if already set, and thus fix crash with
many ballons.
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