Optimise some pagevec functions by not reenabling irqs while
switching lru locks.

Index: linux-2.6/mm/swap.c
===================================================================
--- linux-2.6.orig/mm/swap.c
+++ linux-2.6/mm/swap.c
@@ -220,10 +220,13 @@ void release_pages(struct page **pages, 
 
 		pagezone = page_zone(page);
 		if (pagezone != zone) {
-			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+			spin_lock_prefetch(&pagezone->lru_lock);
+			if (!zone)
+				local_irq_disable();
+			else
+				spin_unlock(&zone->lru_lock);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock(&zone->lru_lock);
 		}
 		if (TestClearPageLRU(page))
 			del_page_from_lru(zone, page);
@@ -296,10 +299,12 @@ void __pagevec_lru_add(struct pagevec *p
 		struct zone *pagezone = page_zone(page);
 
 		if (pagezone != zone) {
+			if (!zone)
+				local_irq_disable();
 			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock(&zone->lru_lock);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock(&zone->lru_lock);
 		}
 		if (TestSetPageLRU(page))
 			BUG();
@@ -323,10 +328,12 @@ void __pagevec_lru_add_active(struct pag
 		struct zone *pagezone = page_zone(page);
 
 		if (pagezone != zone) {
+			if (!zone)
+				local_irq_disable();
 			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock(&zone->lru_lock);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock(&zone->lru_lock);
 		}
 		if (TestSetPageLRU(page))
 			BUG();