mm: compaction: show gfp flag names in try_to_compact_pages tracepoint

Showing the gfp flag names instead of the gfp_mask makes trace more
convenient.

Link: http://lkml.kernel.org/r/1552527998-13162-1-git-send-email-laoar.shao@gmail.com
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/trace/events/compaction.h

@@ -189,9 +189,9 @@ TRACE_EVENT(mm_compaction_try_to_compact_pages,
 		__entry->prio = prio;
 	),
 
-	TP_printk("order=%d gfp_mask=0x%x priority=%d",
+	TP_printk("order=%d gfp_mask=%s priority=%d",
 		__entry->order,
-		__entry->gfp_mask,
+		show_gfp_flags(__entry->gfp_mask),
 		__entry->prio)
 );