mm: introduce for_each_populated_zone() macro

Impact: cleanup

In almost cases, for_each_zone() is used with populated_zone().  It's
because almost function doesn't need memoryless node information.
Therefore, for_each_populated_zone() can help to make code simplify.

This patch has no functional change.

[akpm@linux-foundation.org: small cleanup]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: 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/mmzone.h

@@ -806,6 +806,14 @@ extern struct zone *next_zone(struct zone *zone);
 	     zone;					\
 	     zone = next_zone(zone))
 
+#define for_each_populated_zone(zone)		        \
+	for (zone = (first_online_pgdat())->node_zones; \
+	     zone;					\
+	     zone = next_zone(zone))			\
+		if (!populated_zone(zone))		\
+			; /* do nothing */		\
+		else
+
 static inline struct zone *zonelist_zone(struct zoneref *zoneref)
 {
 	return zoneref->zone;

kernel/power/snapshot.c

@@ -321,13 +321,10 @@ static int create_mem_extents(struct list_head *list, gfp_t gfp_mask)
 
 	INIT_LIST_HEAD(list);
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
 		unsigned long zone_start, zone_end;
 		struct mem_extent *ext, *cur, *aux;
 
-		if (!populated_zone(zone))
-			continue;
-
 		zone_start = zone->zone_start_pfn;
 		zone_end = zone->zone_start_pfn + zone->spanned_pages;
 
@@ -804,8 +801,8 @@ static unsigned int count_free_highmem_pages(void)
 	struct zone *zone;
 	unsigned int cnt = 0;
 
-	for_each_zone(zone)
+	for_each_populated_zone(zone)
-		if (populated_zone(zone) && is_highmem(zone))
+		if (is_highmem(zone))
 			cnt += zone_page_state(zone, NR_FREE_PAGES);
 
 	return cnt;

kernel/power/swsusp.c

@@ -229,17 +229,16 @@ int swsusp_shrink_memory(void)
 		size = count_data_pages() + PAGES_FOR_IO + SPARE_PAGES;
 		tmp = size;
 		size += highmem_size;
-		for_each_zone (zone)
+		for_each_populated_zone(zone) {
-			if (populated_zone(zone)) {
+			tmp += snapshot_additional_pages(zone);
-				tmp += snapshot_additional_pages(zone);
+			if (is_highmem(zone)) {
-				if (is_highmem(zone)) {
+				highmem_size -=
-					highmem_size -=
 					zone_page_state(zone, NR_FREE_PAGES);
-				} else {
+			} else {
-					tmp -= zone_page_state(zone, NR_FREE_PAGES);
+				tmp -= zone_page_state(zone, NR_FREE_PAGES);
-					tmp += zone->lowmem_reserve[ZONE_NORMAL];
+				tmp += zone->lowmem_reserve[ZONE_NORMAL];
-				}
 			}
+		}
 
 		if (highmem_size < 0)
 			highmem_size = 0;

mm/page_alloc.c

@@ -922,13 +922,10 @@ static void drain_pages(unsigned int cpu)
 	unsigned long flags;
 	struct zone *zone;
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
 		struct per_cpu_pageset *pset;
 		struct per_cpu_pages *pcp;
 
-		if (!populated_zone(zone))
-			continue;
-
 		pset = zone_pcp(zone, cpu);
 
 		pcp = &pset->pcp;
@@ -1879,10 +1876,7 @@ void show_free_areas(void)
 	int cpu;
 	struct zone *zone;
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
-		if (!populated_zone(zone))
-			continue;
-
 		show_node(zone);
 		printk("%s per-cpu:\n", zone->name);
 
@@ -1922,12 +1916,9 @@ void show_free_areas(void)
 		global_page_state(NR_PAGETABLE),
 		global_page_state(NR_BOUNCE));
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
 		int i;
 
-		if (!populated_zone(zone))
-			continue;
-
 		show_node(zone);
 		printk("%s"
 			" free:%lukB"
@@ -1967,12 +1958,9 @@ void show_free_areas(void)
 		printk("\n");
 	}
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
  		unsigned long nr[MAX_ORDER], flags, order, total = 0;
 
-		if (!populated_zone(zone))
-			continue;
-
 		show_node(zone);
 		printk("%s: ", zone->name);
 
@@ -2784,11 +2772,7 @@ static int __cpuinit process_zones(int cpu)
 
 	node_set_state(node, N_CPU);	/* this node has a cpu */
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
-
-		if (!populated_zone(zone))
-			continue;
-
 		zone_pcp(zone, cpu) = kmalloc_node(sizeof(struct per_cpu_pageset),
 					 GFP_KERNEL, node);
 		if (!zone_pcp(zone, cpu))

mm/vmscan.c

@@ -2061,11 +2061,9 @@ static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
 	struct zone *zone;
 	unsigned long ret = 0;
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
 		enum lru_list l;
 
-		if (!populated_zone(zone))
-			continue;
 		if (zone_is_all_unreclaimable(zone) && prio != DEF_PRIORITY)
 			continue;
 

mm/vmstat.c

@@ -135,11 +135,7 @@ static void refresh_zone_stat_thresholds(void)
 	int cpu;
 	int threshold;
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
-
-		if (!zone->present_pages)
-			continue;
-
 		threshold = calculate_threshold(zone);
 
 		for_each_online_cpu(cpu)
@@ -301,12 +297,9 @@ void refresh_cpu_vm_stats(int cpu)
 	int i;
 	int global_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
 
-	for_each_zone(zone) {
+	for_each_populated_zone(zone) {
 		struct per_cpu_pageset *p;
 
-		if (!populated_zone(zone))
-			continue;
-
 		p = zone_pcp(zone, cpu);
 
 		for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)