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

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Message-ID: <20120823160647.GA10777@t510.redhat.com>
Date:	Thu, 23 Aug 2012 13:06:48 -0300
From:	Rafael Aquini <aquini@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	"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>,
	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 Thu, Aug 23, 2012 at 12:03:15PM -0400, Rik van Riel wrote:
> >
> >Not "longer" - apparently forever unless user resend the leak command.
> >It's wrong - it should
> >1. not tell host if nothing was done
> >2. after migration finished leak and tell host
> 
> Agreed.  If the balloon is told to leak N pages, and could
> not do so because those pages were locked, the balloon driver
> needs to retry (maybe waiting on a page lock?) and not signal
> completion until after the job has been completed.
> 
> Having the balloon driver wait on the page lock should be
> fine, because compaction does not hold the page lock for
> long.

And that is precisely what leak_balloon is doing. When it stumbles across a
locked page it gets rid of that leak round to give a shot for compaction to
finish its task.


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