mm: compaction: abort compaction loop if lock is contended or run too long

mm: compaction: abort compaction loop if lock is contended or run too long

isolate_migratepages_range() might isolate no pages, for example, when
zone->lru_lock is contended and compaction is async.  In this case, we
should abort compaction, otherwise, compact_zone will run a useless loop
and make zone->lru_lock is even contended.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Shaohua Li <shli@fusionio.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>