mm: enable CONFIG_COMPACTION by default

Now that lumpy reclaim has been removed, compaction is the only way left
to free up contiguous memory areas.  It is time to just enable
CONFIG_COMPACTION by default.
Signed-off-by: NRik van Riel <riel@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Acked-by: NRafael Aquini <aquini@redhat.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/Kconfig

@@ -191,6 +191,7 @@ config SPLIT_PTLOCK_CPUS
 # support for memory compaction
 config COMPACTION
 	bool "Allow for memory compaction"
+	def_bool y
 	select MIGRATION
 	depends on MMU
 	help