linux-kernel - Re: [PATCH v9 0/5] make balloon pages movable by compaction

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Message-ID: <20120826154423.GA15478@redhat.com>
Date:	Sun, 26 Aug 2012 18:44:23 +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>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v9 0/5] make balloon pages movable by compaction

On Sun, Aug 26, 2012 at 10:40:37AM -0400, Rik van Riel wrote:
> On 08/26/2012 03:58 AM, Michael S. Tsirkin wrote:
> >On Sat, Aug 25, 2012 at 02:24:55AM -0300, Rafael Aquini 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
> >
> >Meta-question: are there any numbers showing gain from this patchset?
> >
> >The reason I ask, on migration we notify host about each page
> >individually.  If this is rare maybe the patchset does not help much.
> >If this is common we would be better off building up a list of multiple
> >pages and passing them in one go.
> 
> The gain is in getting a better THP allocation rate inside the
> guest, allowing applications to run faster.
> 
> The rarer it is for this code to run, the better - it means we
> are getting the benefits without the overhead :)

I am simply asking how was this patchset tested.
It would be nice to have this info in commit log.
Since this is an optimization patch it is strange
to see one with no numbers at all.
For example, you probably run some workload and
played with the balloon, and then saw less huge pages
without the patch and more with?
Please put this info in the cover letter.

> -- 
> All rights reversed
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