mm, compaction: abstract compaction feedback to helpers

Compaction can provide a wild variation of feedback to the caller.  Many
of them are implementation specific and the caller of the compaction
(especially the page allocator) shouldn't be bound to specifics of the
current implementation.

This patch abstracts the feedback into three basic types:
	- compaction_made_progress - compaction was active and made some
	  progress.
	- compaction_failed - compaction failed and further attempts to
	  invoke it would most probably fail and therefore it is not
	  worth retrying
	- compaction_withdrawn - compaction wasn't invoked for an
          implementation specific reasons. In the current implementation
          it means that the compaction was deferred, contended or the
          page scanners met too early without any progress. Retrying is
          still worthwhile.

[vbabka@suse.cz: do not change thp back off behavior]
[akpm@linux-foundation.org: fix typo in comment, per Hillf]
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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