Optional DMA zone: Replace uses of ZONE_DMA as the first zone

In two places in the VM we use ZONE_DMA to refer to the first zone.
If ZONE_DMA is optional then other zones may be first. So simply
replace ZONE_DMA with zone 0.

This also fixes ZONETABLE_PGSHIFT. If we have only a single zone then
ZONES_PGSHIFT may become 0 because there is no need anymore to encode the
zone number related to a pgdat. However, we still need a zonetable to index
all the zones for each node if this is a NUMA system. Therefore define
ZONETABLE_SHIFT unconditionally as the offset of the ZONE field in page flags.

Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm2/mm/mempolicy.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/mempolicy.c	2006-09-18 21:16:32.000000000 -0500
+++ linux-2.6.18-rc6-mm2/mm/mempolicy.c	2006-09-18 21:17:23.067526840 -0500
@@ -105,7 +105,7 @@ static struct kmem_cache *sn_cache;
 
 /* Highest zone. An specific allocation for a zone below that is not
    policied. */
-enum zone_type policy_zone = ZONE_DMA;
+enum zone_type policy_zone = 0;
 
 struct mempolicy default_policy = {
 	.refcnt = ATOMIC_INIT(1), /* never free it */
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 21:17:16.000000000 -0500
+++ linux-2.6.18-rc6-mm2/mm/page_alloc.c	2006-09-18 21:17:23.086083065 -0500
@@ -2466,11 +2466,11 @@ static void __meminit free_area_init_cor
 				"  %s zone: %lu pages exceeds realsize %lu\n",
 				zone_names[j], memmap_pages, realsize);
 
-		/* Account for reserved DMA pages */
-		if (j == ZONE_DMA && realsize > dma_reserve) {
+		/* Account for reserved pages */
+		if (j == 0 && realsize > dma_reserve) {
 			realsize -= dma_reserve;
-			printk(KERN_DEBUG "  DMA zone: %lu pages reserved\n",
-								dma_reserve);
+			printk(KERN_DEBUG "  %s zone: %lu pages reserved\n",
+					zone_names[0], dma_reserve);
 		}
 
 		if (!is_highmem_idx(j))
Index: linux-2.6.18-rc6-mm2/include/linux/mm.h
===================================================================
--- linux-2.6.18-rc6-mm2.orig/include/linux/mm.h	2006-09-18 21:17:12.000000000 -0500
+++ linux-2.6.18-rc6-mm2/include/linux/mm.h	2006-09-18 21:17:45.584040140 -0500
@@ -418,7 +418,7 @@ void split_page(struct page *page, unsig
 #else
 #define ZONEID_SHIFT		(NODES_SHIFT + ZONES_SHIFT)
 #endif
-#define ZONEID_PGSHIFT		ZONES_PGSHIFT
+#define ZONEID_PGSHIFT		ZONES_PGOFF
 
 #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED
 #error SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED