linux-kernel - Re: [PATCH v10 0/5] make balloon pages movable by compaction

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Message-Id: <20120917151531.e9ac59f2.akpm@linux-foundation.org>
Date:	Mon, 17 Sep 2012 15:15:31 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
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>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Andi Kleen <andi@...stfloor.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Minchan Kim <minchan@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v10 0/5] make balloon pages movable by compaction

On Mon, 17 Sep 2012 13:38:15 -0300
Rafael Aquini <aquini@...hat.com> wrote:

> Memory fragmentation introduced by ballooning might reduce significantly
> the number of 2MB contiguous memory blocks that can be used within a guest,
> thus imposing performance penalties associated with the reduced number of
> transparent huge pages that could be used by the guest workload.
> 
> This patch-set follows the main idea discussed at 2012 LSFMMS session:
> "Ballooning for transparent huge pages" -- http://lwn.net/Articles/490114/
> to introduce the required changes to the virtio_balloon driver, as well as
> the changes to the core compaction & migration bits, in order to make those
> subsystems aware of ballooned pages and allow memory balloon pages become
> movable within a guest, thus avoiding the aforementioned fragmentation issue
> 
> Following are numbers that prove this patch benefits on allowing compaction
> to be more effective at memory ballooned guests.
> 
> Results for STRESS-HIGHALLOC benchmark, from Mel Gorman's mmtests suite,
> running on a 4gB RAM KVM guest which was ballooning 1gB RAM in 256mB chunks,
> at every minute (inflating/deflating), while test was running:

How can a patchset reach v10 and have zero Reviewed-by's?

The patchset looks reasonable to me and your empirical results look
good.  But I don't feel that I'm in a position to decide on its overall
desirability, either in a standalone sense or in comparison to any
alternative schemes which anyone has proposed.

IOW, Rusty and KVM folks: please consider thyself poked.

I looked through the code and have some comments which are minor in the
overall scheme of things.  I'll be more comfortable when a compaction
expert has had a go over it.  IOW, Mel joins the pokee list ;)

(The question of "overall desirability" is the big one here.  Do we
actually want to add this to Linux?  The rest is details which we can
work out).


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