ZVC: overcompensate while incrementing ZVC counters

Overcompensate by a balance factor when incrementing or decrementing
ZVC counters anticipating continual increase in the same direction.

Note that I have not (yet) been able to see any effect off this approach on
an 8p system where I tested this.
I probably will have a chance to test it on larger systems (160p) tomorrow.

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

Index: linux-2.6.17-mm4/mm/vmstat.c
===================================================================
--- linux-2.6.17-mm4.orig/mm/vmstat.c	2006-06-29 13:34:13.130103415 -0700
+++ linux-2.6.17-mm4/mm/vmstat.c	2006-06-30 09:44:42.106442018 -0700
@@ -182,6 +182,9 @@ EXPORT_SYMBOL(mod_zone_page_state);
  * in between and therefore the atomicity vs. interrupt cannot be exploited
  * in a useful way here.
  */
+
+#define balance_factor (STAT_THRESHOLD / 2)
+
 static void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
 {
 	s8 *p = diff_pointer(zone, item);
@@ -189,8 +192,8 @@ static void __inc_zone_state(struct zone
 	(*p)++;
 
 	if (unlikely(*p > STAT_THRESHOLD)) {
-		zone_page_state_add(*p, zone, item);
-		*p = 0;
+		zone_page_state_add(*p + balance_factor, zone, item);
+		*p = -balance_factor;
 	}
 }
 
@@ -208,8 +211,8 @@ void __dec_zone_page_state(struct page *
 	(*p)--;
 
 	if (unlikely(*p < -STAT_THRESHOLD)) {
-		zone_page_state_add(*p, zone, item);
-		*p = 0;
+		zone_page_state_add(*p - balance_factor, zone, item);
+		*p = balance_factor;
 	}
 }
 EXPORT_SYMBOL(__dec_zone_page_state);