mm: introduce a common interface for balloon pages mobility fix

mm: introduce a common interface for balloon pages mobility fix

It's useful to keep memory defragmented so that all high-order page
allocations have a chance to succeed, not simply transparent hugepages.
Thus, allow balloon compaction for any system with memory compaction
enabled, which is the defconfig.

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>