On Fri, 2 Oct 2009 13:44:58 -0500
Robert Jennings [off-list ref] wrote:

Memory balloon drivers can allocate a large amount of memory which
is not movable but could be freed to accomodate memory hotplug remove.

Prior to calling the memory hotplug notifier chain the memory in the
pageblock is isolated.  If the migrate type is not MIGRATE_MOVABLE the
isolation will not proceed, causing the memory removal for that page
range to fail.

Rather than failing pageblock isolation if the the migrateteype is not
MIGRATE_MOVABLE, this patch checks if all of the pages in the pageblock
are owned by a registered balloon driver (or other entity) using a
notifier chain.  If all of the non-movable pages are owned by a balloon,
they can be freed later through the memory notifier chain and the range
can still be isolated in set_migratetype_isolate().

The patch looks sane enough to me.

I expect that if the powerpc and s390 guys want to work on CMM over the
next couple of months, they'd like this patch merged into 2.6.32.  It's
a bit larger and more involved than one would like, but I guess we can
do that if suitable people (Mel?  Kamezawa?) have had a close look and
are OK with it.

What do people think?

Has it been carefully compile- and run-time tested with
CONFIG_MEMORY_HOTPLUG_SPARSE=n?