sched, numa, mm: Add last_cpu to page flags

sched, numa, mm: Add last_cpu to page flags

Introduce a per-page last_cpu field, fold this into the struct
page::flags field whenever possible.

The unlikely/rare 32bit NUMA configs will likely grow the page-frame.

[ Completely dropping 32bit support for CONFIG_NUMA_BALANCING would simplify
  things, but it would also remove the warning if we grow enough 64bit
  only page-flags to push the last-cpu out. ]

Suggested-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>