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

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Date:	Mon, 17 Sep 2012 18:45:32 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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>,
	"Michael S. Tsirkin" <mst@...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 09/17/2012 06:15 PM, Andrew Morton wrote:
> 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?

Because people kept finding issues and nitpicks in patch 1/5,
which kept people from putting their Reviewed-by's on the other
patches :)

> (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).

I believe we absolutely want this, to increase the likelyhood
of being able to use THP in KVM guests, which is exactly
where THP gives the largest performance benefit.

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