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>

include/linux/mm.h

@@ -1053,6 +1053,7 @@ extern void set_dma_reserve(unsigned long new_dma_reserve);
 extern void memmap_init_zone(unsigned long, int, unsigned long,
 				unsigned long, enum memmap_context);
 extern void setup_per_zone_wmarks(void);
+extern void calculate_zone_inactive_ratio(struct zone *zone);
 extern void mem_init(void);
 extern void __init mmap_init(void);
 extern void show_mem(void);

mm/page_alloc.c

@@ -4478,22 +4478,26 @@ void setup_per_zone_wmarks(void)
  *    1TB     101        10GB
  *   10TB     320        32GB
  */
-static void __init setup_per_zone_inactive_ratio(void)
+void calculate_zone_inactive_ratio(struct zone *zone)
 {
-	struct zone *zone;
+	unsigned int gb, ratio;
 
-	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 size in gigabytes */
-		gb = zone->present_pages >> (30 - PAGE_SHIFT);
-		if (gb)
-			ratio = int_sqrt(10 * gb);
-		else
-			ratio = 1;
+	zone->inactive_ratio = ratio;
+}
 
-		zone->inactive_ratio = ratio;
-	}
+static void __init setup_per_zone_inactive_ratio(void)
+{
+	struct zone *zone;
+
+	for_each_zone(zone)
+		calculate_zone_inactive_ratio(zone);
 }
 
 /*