page-allocator: add inactive ratio calculation function of each zone

Factor the per-zone arithemetic inside setup_per_zone_inactive_ratio()'s
loop into a a separate function, calculate_zone_inactive_ratio().  This
function will be used in a later patch

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8629c84..303607f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4478,22 +4478,26 @@
  *    1TB     101        10GB
  *   10TB     320        32GB
  */
+void calculate_zone_inactive_ratio(struct zone *zone)
+{
+	unsigned int gb, ratio;
+
+	/* Zone size in gigabytes */
+	gb = zone->present_pages >> (30 - PAGE_SHIFT);
+	if (gb)
+		ratio = int_sqrt(10 * gb);
+	else
+		ratio = 1;
+
+	zone->inactive_ratio = ratio;
+}
+
 static void __init setup_per_zone_inactive_ratio(void)
 {
 	struct zone *zone;
 
-	for_each_zone(zone) {
-		unsigned int gb, ratio;
-
-		/* Zone size in gigabytes */
-		gb = zone->present_pages >> (30 - PAGE_SHIFT);
-		if (gb)
-			ratio = int_sqrt(10 * gb);
-		else
-			ratio = 1;
-
-		zone->inactive_ratio = ratio;
-	}
+	for_each_zone(zone)
+		calculate_zone_inactive_ratio(zone);
 }
 
 /*