Singe zone per pdat optimization

If we only have a single zone per node / pgdat then we do not need
the zone_pgdat link but can directly calculate the pgdat address
from zone since pgdat embedds the zone struct. This avoids one
indirection on critical VM paths.

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

Index: linux-2.6.18-rc6-mm2/include/linux/mmzone.h
===================================================================
--- linux-2.6.18-rc6-mm2.orig/include/linux/mmzone.h	2006-09-18 21:27:55.000000000 -0500
+++ linux-2.6.18-rc6-mm2/include/linux/mmzone.h	2006-09-18 21:27:59.343896203 -0500
@@ -282,7 +282,12 @@ struct zone {
 	/*
 	 * Discontig memory support fields.
 	 */
+#ifdef MULTI_ZONE
 	struct pglist_data	*zone_pgdat;
+#define get_pgdat(__zone)	((__zone)->zone_pgdat)
+#else
+#define get_pgdat(__zone) container_of((__zone), struct pglist_data, node_zones[0])
+#endif
 	/* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */
 	unsigned long		zone_start_pfn;
 
Index: linux-2.6.18-rc6-mm2/mm/page_alloc.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/page_alloc.c	2006-09-18 21:27:54.000000000 -0500
+++ linux-2.6.18-rc6-mm2/mm/page_alloc.c	2006-09-18 21:27:59.365382353 -0500
@@ -960,7 +960,7 @@ get_page_from_freelist(gfp_t gfp_mask, u
 	do {
 		zone = *z;
 		if (unlikely(NUMA_BUILD && (gfp_mask & __GFP_THISNODE) &&
-			zone->zone_pgdat != zonelist->zones[0]->zone_pgdat))
+			pgdat(zone) != pgdat(zonelist->zones[0])))
 				break;
 		if ((alloc_flags & ALLOC_CPUSET) &&
 				!cpuset_zone_allowed(zone, gfp_mask))
@@ -1996,7 +1996,7 @@ static __meminit
 int zone_wait_table_init(struct zone *zone, unsigned long zone_size_pages)
 {
 	int i;
-	struct pglist_data *pgdat = zone->zone_pgdat;
+	struct pglist_data *pgdat = get_pgdat(zone);
 	size_t alloc_size;
 
 	/*
@@ -2058,7 +2058,7 @@ __meminit int init_currently_empty_zone(
 					unsigned long zone_start_pfn,
 					unsigned long size)
 {
-	struct pglist_data *pgdat = zone->zone_pgdat;
+	struct pglist_data *pgdat = get_pgdat(zone);
 	int ret;
 	ret = zone_wait_table_init(zone, size);
 	if (ret)
@@ -2500,7 +2500,9 @@ static void __meminit free_area_init_cor
 		spin_lock_init(&zone->lock);
 		spin_lock_init(&zone->lru_lock);
 		zone_seqlock_init(zone);
+#ifdef MULTI_ZONE
 		zone->zone_pgdat = pgdat;
+#endif
 		zone->free_pages = 0;
 
 		zone->temp_priority = zone->prev_priority = DEF_PRIORITY;
Index: linux-2.6.18-rc6-mm2/mm/vmscan.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/vmscan.c	2006-09-18 21:24:39.000000000 -0500
+++ linux-2.6.18-rc6-mm2/mm/vmscan.c	2006-09-18 21:27:59.380032001 -0500
@@ -1299,7 +1299,7 @@ void wakeup_kswapd(struct zone *zone, in
 	if (!populated_zone(zone))
 		return;
 
-	pgdat = zone->zone_pgdat;
+	pgdat = get_pgdat(zone);
 	if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
 		return;
 	if (pgdat->kswapd_max_order < order)
Index: linux-2.6.18-rc6-mm2/mm/mmzone.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/mmzone.c	2006-09-18 21:24:40.000000000 -0500
+++ linux-2.6.18-rc6-mm2/mm/mmzone.c	2006-09-18 21:27:59.406401367 -0500
@@ -32,11 +32,14 @@ EXPORT_UNUSED_SYMBOL(next_online_pgdat);
  */
 struct zone *next_zone(struct zone *zone)
 {
-	pg_data_t *pgdat = zone->zone_pgdat;
+	pg_data_t *pgdat = get_pgdat(zone);
 
+#ifdef MULTI_ZONE
 	if (zone < pgdat->node_zones + MAX_NR_ZONES - 1)
 		zone++;
-	else {
+	else
+#endif
+	{
 		pgdat = next_online_pgdat(pgdat);
 		if (pgdat)
 			zone = pgdat->node_zones;
Index: linux-2.6.18-rc6-mm2/mm/sparse.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/sparse.c	2006-09-18 21:24:40.000000000 -0500
+++ linux-2.6.18-rc6-mm2/mm/sparse.c	2006-09-18 21:27:59.415191155 -0500
@@ -297,7 +297,7 @@ int sparse_add_one_section(struct zone *
 			   int nr_pages)
 {
 	unsigned long section_nr = pfn_to_section_nr(start_pfn);
-	struct pglist_data *pgdat = zone->zone_pgdat;
+	struct pglist_data *pgdat = get_pgdat(zone);
 	struct mem_section *ms;
 	struct page *memmap;
 	unsigned long flags;