mm/compaction.c: add an is_via_compact_memory() helper

Introduce is_via_compact_memory() helper indicating compacting via
/proc/sys/vm/compact_memory to improve readability.

To catch this situation in __compaction_suitable, use order as parameter
directly instead of using struct compact_control.

This patch has no functional changes.

Signed-off-by: Yaowei Bai <bywxiaobai@163.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/compaction.c

@@ -1197,6 +1197,15 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
 }
 
+/*
+ * order == -1 is expected when compacting via
+ * /proc/sys/vm/compact_memory
+ */
+static inline bool is_via_compact_memory(int order)
+{
+	return order == -1;
+}
+
 static int __compact_finished(struct zone *zone, struct compact_control *cc,
 			    const int migratetype)
 {
@@ -1223,11 +1232,7 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc,
 		return COMPACT_COMPLETE;
 	}
 
-	/*
-	 * order == -1 is expected when compacting via
-	 * /proc/sys/vm/compact_memory
-	 */
-	if (cc->order == -1)
+	if (is_via_compact_memory(cc->order))
 		return COMPACT_CONTINUE;
 
 	/* Compaction run is not finished if the watermark is not met */
@@ -1290,11 +1295,7 @@ static unsigned long __compaction_suitable(struct zone *zone, int order,
 	int fragindex;
 	unsigned long watermark;
 
-	/*
-	 * order == -1 is expected when compacting via
-	 * /proc/sys/vm/compact_memory
-	 */
-	if (order == -1)
+	if (is_via_compact_memory(order))
 		return COMPACT_CONTINUE;
 
 	watermark = low_wmark_pages(zone);
@@ -1658,10 +1659,11 @@ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
 		 * this makes sure we compact the whole zone regardless of
 		 * cached scanner positions.
 		 */
-		if (cc->order == -1)
+		if (is_via_compact_memory(cc->order))
 			__reset_isolation_suitable(zone);
 
-		if (cc->order == -1 || !compaction_deferred(zone, cc->order))
+		if (is_via_compact_memory(cc->order) ||
+				!compaction_deferred(zone, cc->order))
 			compact_zone(zone, cc);
 
 		if (cc->order > 0) {