free_area[] bitmap elimination[1/3]

diff -puN mm/page_alloc.c~eliminate-bitmap-init mm/page_alloc.c
@@ -301,7 +301,7 @@ void __free_pages_ok(struct page *page, 
  * subsystem according to empirical testing, and this is also justified
  * by considering the behavior of a buddy system containing a single
  * large block of memory acted on by a series of small allocations.
- * This behavior is a critical factor in sglist merging's success.
+ * This behavior is a critical factor in s merging's success.
  *
  * -- wli
  */

@@ -1499,6 +1499,25 @@ static void __init calculate_zone_totalp
 	printk(KERN_DEBUG "On node %d totalpages: %lu\n", pgdat->node_id, realtotalpages);
 }
 
+/*   
+ *    calculate_aligned_order()
+ *    this function calculates an upper bound order of alignment of buddy pages.
+ *    if order < zone->aligned_order, every page are guaranteed to have its buddy.
+ */
+void __init calculate_aligned_order(int nid, int zone, unsigned long start_pfn, 
+				    unsigned long size)
+{
+	int order;
+	unsigned long mask;
+	struct zone *zonep = zone_table[NODEZONE(nid, zone)];
+	for (order = 0 ; order < MAX_ORDER; order++) {
+		mask = (unsigned long)1 << order;
+		if ((start_pfn & mask) || (size & mask))
+			break;
+	}
+	if (order < zonep->aligned_order)
+		zonep->aligned_order = order;
+}
 
 /*
  * Initially all pages are reserved - free ones are freed

@@ -1510,7 +1529,7 @@ void __init memmap_init_zone(unsigned lo
 {
 	struct page *start = pfn_to_page(start_pfn);
 	struct page *page;
-
+	unsigned long saved_start_pfn = start_pfn;
 	for (page = start; page < (start + size); page++) {
 		set_page_zone(page, NODEZONE(nid, zone));
 		set_page_count(page, 0);

@@ -1524,51 +1543,18 @@ void __init memmap_init_zone(unsigned lo
 #endif
 		start_pfn++;
 	}
-}
-
-/*
- * Page buddy system uses "index >> (i+1)", where "index" is
- * at most "size-1".
- *
- * The extra "+3" is to round down to byte size (8 bits per byte
- * assumption). Thus we get "(size-1) >> (i+4)" as the last byte
- * we can access.
- *
- * The "+1" is because we want to round the byte allocation up
- * rather than down. So we should have had a "+7" before we shifted
- * down by three. Also, we have to add one as we actually _use_ the
- * last bit (it's [0,n] inclusive, not [0,n[).
- *
- * So we actually had +7+1 before we shift down by 3. But
- * (n+8) >> 3 == (n >> 3) + 1 (modulo overflows, which we do not have).
- *
- * Finally, we LONG_ALIGN because all bitmap operations are on longs.
- */
-unsigned long pages_to_bitmap_size(unsigned long order, unsigned long nr_pages)
-{
-	unsigned long bitmap_size;
-
-	bitmap_size = (nr_pages-1) >> (order+4);
-	bitmap_size = LONG_ALIGN(bitmap_size+1);
-
-	return bitmap_size;
+	/* Because memmap_init_zone() is called in suitable way 
+	 * even if zone has memory hole,
+	 * calling calculate_aligned_order(zone) here is reasonable 
+	 */
+	calculate_aligned_order(nid, zone, saved_start_pfn, size);
 }
 
 void zone_init_free_lists(struct pglist_data *pgdat, struct zone *zone, unsigned long size)
 {
 	int order;
-	for (order = 0; ; order++) {
-		unsigned long bitmap_size;
-
+	for (order = 0 ; order < MAX_ORDER ; order++) {
 		INIT_LIST_HEAD(&zone->free_area[order].free_list);
-		if (order == MAX_ORDER-1) {
-			zone->free_area[order].map = NULL;
-			break;
-		}
-
-		bitmap_size = pages_to_bitmap_size(order, size);
-		zone->free_area[order].map =
-		  (unsigned long *) alloc_bootmem_node(pgdat, bitmap_size);
 	}
 }
 

@@ -1681,11 +1667,9 @@ static void __init free_area_init_core(s
 
 		if ((zone_start_pfn) & (zone_required_alignment-1))
 			printk("BUG: wrong zone alignment, it will crash\n");
-
+		zone->aligned_order = MAX_ORDER;
 		memmap_init(size, nid, j, zone_start_pfn);
-
 		zone_start_pfn += size;
-
 		zone_init_free_lists(pgdat, zone, zone->spanned_pages);
 	}
 }