On 09/17/2012 06:15 PM, Andrew Morton wrote:

On Mon, 17 Sep 2012 13:38:15 -0300
Rafael Aquini [off-list ref] wrote:

quoted

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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