mm/compaction.c: __compact_pgdat() code cleanuup

This patch uses is_via_compact_memory() to distinguish compaction from
sysfs or sysctl.  And, this patch also reduces indentation on
compaction_defer_reset() by filtering these cases first before checking
watermark.

There is no functional change.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/compaction.c

@@ -1658,15 +1658,16 @@ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
 				!compaction_deferred(zone, cc->order))
 			compact_zone(zone, cc);
 
-		if (cc->order > 0) {
+		VM_BUG_ON(!list_empty(&cc->freepages));
+		VM_BUG_ON(!list_empty(&cc->migratepages));
+
+		if (is_via_compact_memory(cc->order))
+			continue;
+
 		if (zone_watermark_ok(zone, cc->order,
 				low_wmark_pages(zone), 0, 0))
 			compaction_defer_reset(zone, cc->order, false);
 	}
-
-		VM_BUG_ON(!list_empty(&cc->freepages));
-		VM_BUG_ON(!list_empty(&cc->migratepages));
-	}
 }
 
 void compact_pgdat(pg_data_t *pgdat, int order)