Scale ZVC threshold to the size of a zone.

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

Index: linux-2.6.18-rc1-mm1/mm/vmstat.c
===================================================================
--- linux-2.6.18-rc1-mm1.orig/mm/vmstat.c	2006-07-10 10:33:44.369581118 -0700
+++ linux-2.6.18-rc1-mm1/mm/vmstat.c	2006-07-11 11:46:02.834904544 -0700
@@ -112,38 +112,58 @@ void vm_events_fold_cpu(int cpu)
 atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
 EXPORT_SYMBOL(vm_stat);
 
+void zap_zone_vm_stats(struct zone *zone)
+{
+	int cpu;
+	int threshold;
+	int mb;
+
+	memset(zone->vm_stat, 0, sizeof(zone->vm_stat));
 #ifdef CONFIG_SMP
 
-#define STAT_THRESHOLD 32
+	/*
+	 * Increase the threshold for every 4 Megabyte of memory by one.
+	 * The bigger the zone the more flexibility we can give us.
+	 *
+	 * 16MB DMA zone = 4      16*x -y  = 4
+	 * 1GB 1024MB = 32 	1024*x -y  = 32
+	 * The minimum threshold of 4 is equal to 256 MB of memory.
+	 * The maximum of 125 reflects 8 Gigabytes.
+	 *
+	 * The inaccuracy per cpu introduced to a counter is < 0.1%.
+	 */
+	mb = zone->present_pages >> (20 - PAGE_SHIFT);	/* Convert to Megabyte */
+	threshold = (mb - 8) / 2;
+
+	/*
+	 * Threshold must be between 4 and 125
+	 */
+	threshold = max(4, min(125, threshold));
 
-/*
- * Determine pointer to currently valid differential byte given a zone and
- * the item number.
- *
- * Preemption must be off
- */
-static inline s8 *diff_pointer(struct zone *zone, enum zone_stat_item item)
-{
-	return &zone_pcp(zone, smp_processor_id())->vm_stat_diff[item];
+	for_each_possible_cpu(cpu)
+		zone_pcp(zone, cpu)->stat_threshold = threshold;
+#endif
 }
 
+
+#ifdef CONFIG_SMP
+
 /*
  * For use when we know that interrupts are disabled.
  */
 void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 				int delta)
 {
-	s8 *p;
+	struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
+	s8 *p = pcp->vm_stat_diff + item;
 	long x;
 
-	p = diff_pointer(zone, item);
 	x = delta + *p;
 
-	if (unlikely(x > STAT_THRESHOLD || x < -STAT_THRESHOLD)) {
+	if (unlikely(x > pcp->stat_threshold || x < -pcp->stat_threshold)) {
 		zone_page_state_add(x, zone, item);
 		x = 0;
 	}
-
 	*p = x;
 }
 EXPORT_SYMBOL(__mod_zone_page_state);
@@ -185,11 +205,12 @@ EXPORT_SYMBOL(mod_zone_page_state);
  */
 static void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
 {
-	s8 *p = diff_pointer(zone, item);
+	struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
+	s8 *p = pcp->vm_stat_diff + item;
 
 	(*p)++;
 
-	if (unlikely(*p > STAT_THRESHOLD)) {
+	if (unlikely(*p > pcp->stat_threshold)) {
 		zone_page_state_add(*p, zone, item);
 		*p = 0;
 	}
@@ -204,11 +225,12 @@ EXPORT_SYMBOL(__inc_zone_page_state);
 void __dec_zone_page_state(struct page *page, enum zone_stat_item item)
 {
 	struct zone *zone = page_zone(page);
-	s8 *p = diff_pointer(zone, item);
+	struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
+	s8 *p = pcp->vm_stat_diff + item;
 
 	(*p)--;
 
-	if (unlikely(*p < -STAT_THRESHOLD)) {
+	if (unlikely(*p < -pcp->stat_threshold)) {
 		zone_page_state_add(*p, zone, item);
 		*p = 0;
 	}
@@ -239,16 +261,12 @@ EXPORT_SYMBOL(inc_zone_page_state);
 void dec_zone_page_state(struct page *page, enum zone_stat_item item)
 {
 	unsigned long flags;
-	struct zone *zone;
-	s8 *p;
+	struct zone *zone = page_zone(page);
+	struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
+	s8 *p = pcp->vm_stat_diff + item;
 
-	zone = page_zone(page);
 	local_irq_save(flags);
-	p = diff_pointer(zone, item);
-
-	(*p)--;
-
-	if (unlikely(*p < -STAT_THRESHOLD)) {
+	if (unlikely(*p < -pcp->stat_threshold)) {
 		zone_page_state_add(*p, zone, item);
 		*p = 0;
 	}
@@ -500,6 +518,7 @@ static int zoneinfo_show(struct seq_file
 		seq_printf(m,
 			   ")"
 			   "\n  pagesets");
+		seq_printf(m, "\n    stat_threshold: %i", zone_pcp(zone, 0)->stat_threshold);
 		for_each_online_cpu(i) {
 			struct per_cpu_pageset *pageset;
 			int j;
Index: linux-2.6.18-rc1-mm1/include/linux/vmstat.h
===================================================================
--- linux-2.6.18-rc1-mm1.orig/include/linux/vmstat.h	2006-07-10 10:33:44.227011832 -0700
+++ linux-2.6.18-rc1-mm1/include/linux/vmstat.h	2006-07-10 13:13:56.724188106 -0700
@@ -163,11 +163,7 @@ extern void zone_statistics(struct zonel
 #define add_zone_page_state(__z, __i, __d) mod_zone_page_state(__z, __i, __d)
 #define sub_zone_page_state(__z, __i, __d) mod_zone_page_state(__z, __i, -(__d))
 
-static inline void zap_zone_vm_stats(struct zone *zone)
-{
-	memset(zone->vm_stat, 0, sizeof(zone->vm_stat));
-}
-
+extern void zap_zone_vm_stats(struct zone *zone);
 extern void inc_zone_state(struct zone *, enum zone_stat_item);
 
 #ifdef CONFIG_SMP
Index: linux-2.6.18-rc1-mm1/include/linux/mmzone.h
===================================================================
--- linux-2.6.18-rc1-mm1.orig/include/linux/mmzone.h	2006-07-10 10:33:44.150844679 -0700
+++ linux-2.6.18-rc1-mm1/include/linux/mmzone.h	2006-07-10 13:13:56.724188106 -0700
@@ -77,6 +77,7 @@ struct per_cpu_pages {
 struct per_cpu_pageset {
 	struct per_cpu_pages pcp[2];	/* 0: hot.  1: cold */
 #ifdef CONFIG_SMP
+	s8 stat_threshold;	/* maximum diff before update */
 	s8 vm_stat_diff[NR_VM_ZONE_STAT_ITEMS];
 #endif
 } ____cacheline_aligned_in_smp;