Single zone vmstat optimizations.

If we have a single zone and the system is not a NUMA system then we
have no need of keeping separate global and per zone statistics. Both
are the same.  So get rid of the statistics in a zone.

The optimization is mainly useful for embedded systems.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-mm2/include/linux/mmzone.h
===================================================================
--- linux-2.6.18-mm2.orig/include/linux/mmzone.h	2006-09-28 16:48:53.752702030 -0500
+++ linux-2.6.18-mm2/include/linux/mmzone.h	2006-09-28 16:49:03.702763441 -0500
@@ -235,8 +235,10 @@ struct zone {
 	/* A count of how many reclaimers are scanning this zone */
 	atomic_t		reclaim_in_progress;
 
+#if defined(CONFIG_NUMA) || defined(MULTI_ZONE)
 	/* Zone statistics */
 	atomic_long_t		vm_stat[NR_VM_ZONE_STAT_ITEMS];
+#endif
 
 	/*
 	 * prev_priority holds the scanning priority for this zone.  It is
Index: linux-2.6.18-mm2/include/linux/vmstat.h
===================================================================
--- linux-2.6.18-mm2.orig/include/linux/vmstat.h	2006-09-28 15:29:45.386200968 -0500
+++ linux-2.6.18-mm2/include/linux/vmstat.h	2006-09-28 16:49:03.712529893 -0500
@@ -105,7 +105,9 @@ extern atomic_long_t vm_stat[NR_VM_ZONE_
 static inline void zone_page_state_add(long x, struct zone *zone,
 				 enum zone_stat_item item)
 {
+#if defined(CONFIG_NUMA) || defined(MULTI_ZONE)
 	atomic_long_add(x, &zone->vm_stat[item]);
+#endif
 	atomic_long_add(x, &vm_stat[item]);
 }
 
@@ -122,11 +124,17 @@ static inline unsigned long global_page_
 static inline unsigned long zone_page_state(struct zone *zone,
 					enum zone_stat_item item)
 {
-	long x = atomic_long_read(&zone->vm_stat[item]);
+	long x;
+
+#if defined(CONFIG_NUMA) || defined(MULTI_ZONE)
+	x = atomic_long_read(&zone->vm_stat[item]);
 #ifdef CONFIG_SMP
 	if (x < 0)
 		x = 0;
 #endif
+#else
+	x = atomic_long_read(&vm_stat[item]);
+#endif
 	return x;
 }
 
@@ -173,7 +181,9 @@ extern void zone_statistics(struct zonel
 
 static inline void zap_zone_vm_stats(struct zone *zone)
 {
+#if defined(CONFIG_NUMA) || defined(MULTI_ZONE)
 	memset(zone->vm_stat, 0, sizeof(zone->vm_stat));
+#endif
 }
 
 extern void inc_zone_state(struct zone *, enum zone_stat_item);
@@ -206,7 +216,9 @@ static inline void __mod_zone_page_state
 
 static inline void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
 {
+#if defined(CONFIG_NUMA) || defined(MULTI_ZONE)
 	atomic_long_inc(&zone->vm_stat[item]);
+#endif
 	atomic_long_inc(&vm_stat[item]);
 }
 
@@ -219,7 +231,9 @@ static inline void __inc_zone_page_state
 static inline void __dec_zone_page_state(struct page *page,
 			enum zone_stat_item item)
 {
+#if defined(CONFIG_NUMA) || defined(MULTI_ZONE)
 	atomic_long_dec(&page_zone(page)->vm_stat[item]);
+#endif
 	atomic_long_dec(&vm_stat[item]);
 }
 
Index: linux-2.6.18-mm2/mm/vmstat.c
===================================================================
--- linux-2.6.18-mm2.orig/mm/vmstat.c	2006-09-28 16:47:53.000000000 -0500
+++ linux-2.6.18-mm2/mm/vmstat.c	2006-09-28 16:52:50.162372945 -0500
@@ -364,7 +364,11 @@ EXPORT_SYMBOL(refresh_vm_stats);
  */
 void zone_statistics(struct zonelist *zonelist, struct zone *z)
 {
+#ifdef MULTI_ZONE
 	if (z->zone_pgdat == zonelist->zones[0]->zone_pgdat) {
+#else
+	if (z == zonelist->zones[0]) {
+#endif
 		__inc_zone_state(z, NUMA_HIT);
 	} else {
 		__inc_zone_state(z, NUMA_MISS);