mm/compaction.c: fix comment for try_to_compact_pages()

"mode" argument is not used by try_to_compact_pages() and sub functions
anymore, it has been replaced by "prio".  Fix the comment to explain the
use of "prio" argument.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Yang Shi <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Yang Shi

mm/compaction.c

@@ -1738,7 +1738,7 @@ int sysctl_extfrag_threshold = 500;
  * @order: The order of the current allocation
  * @alloc_flags: The allocation flags of the current allocation
  * @ac: The context of current allocation
- * @mode: The migration mode for async, sync light, or sync migration
+ * @prio: Determines how hard direct compaction should try to succeed
  *
  * This is the main entry point for direct page compaction.
  */