linux-kernel - Re: [PATCH v8 1/5] mm: introduce a common interface for balloon pages mobility

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Date:	Tue, 21 Aug 2012 22:30:31 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>, 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 v8 1/5] mm: introduce a common interface for balloon
 pages mobility

On Tue, Aug 21, 2012 at 04:23:58PM -0300, Rafael Aquini wrote:
> On Tue, Aug 21, 2012 at 10:13:30PM +0300, Michael S. Tsirkin wrote:
> > > 
> > > I believe rcu_dereference_protected() is what I want/need here, since this code
> > > is always called for pages which we hold locked (PG_locked bit).
> > 
> > It would only help if we locked the page while updating the mapping,
> > as far as I can see we don't.
> >
> 
> But we can do it. In fact, by doing it (locking the page) we can easily avoid
> the nasty race balloon_isolate_page / leak_balloon, in a much simpler way, IMHO.

Absolutely. Further, we should look hard at whether most RCU uses
in this patchset can be replaced with page lock.

-- 
MST
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