From: Bob Picco Andy added code to buddy allocator which does not require the zone's endpoints to be aligned to MAX_ORDER. An issue is that the buddy allocator requires the node_mem_map's endpoints to be MAX_ORDER aligned. Otherwise __page_find_buddy could compute a buddy not in node_mem_map for partial MAX_ORDER regions at zone's endpoints. page_is_buddy will detect that these pages at endpoints are not PG_buddy (they were zeroed out by bootmem allocator and not part of zone). Of course the negative here is we could waste a little memory but the positive is eliminating all the old checks for zone boundary conditions. SPARSEMEM won't encounter this issue because of MAX_ORDER size constraint when SPARSEMEM is configured. ia64 VIRTUAL_MEM_MAP doesn't need the logic either because the holes and endpoints are handled differently. This leaves checking alloc_remap and other arches which privately allocate for node_mem_map. Signed-off-by: Bob Picco Acked-by: Mel Gorman Cc: Dave Hansen Cc: Andy Whitcroft Signed-off-by: Andrew Morton --- include/linux/mmzone.h | 1 + mm/page_alloc.c | 14 +++++++++++--- 2 files changed, 12 insertions(+), 3 deletions(-) diff -puN include/linux/mmzone.h~align-the-node_mem_map-endpoints-to-a-max_order-boundary include/linux/mmzone.h --- devel/include/linux/mmzone.h~align-the-node_mem_map-endpoints-to-a-max_order-boundary 2006-05-19 17:45:00.000000000 -0700 +++ devel-akpm/include/linux/mmzone.h 2006-05-19 17:45:00.000000000 -0700 @@ -22,6 +22,7 @@ #else #define MAX_ORDER CONFIG_FORCE_MAX_ZONEORDER #endif +#define MAX_ORDER_NR_PAGES (1 << (MAX_ORDER - 1)) struct free_area { struct list_head free_list; diff -puN mm/page_alloc.c~align-the-node_mem_map-endpoints-to-a-max_order-boundary mm/page_alloc.c --- devel/mm/page_alloc.c~align-the-node_mem_map-endpoints-to-a-max_order-boundary 2006-05-19 17:45:00.000000000 -0700 +++ devel-akpm/mm/page_alloc.c 2006-05-19 17:45:00.000000000 -0700 @@ -2125,14 +2125,22 @@ static void __init alloc_node_mem_map(st #ifdef CONFIG_FLAT_NODE_MEM_MAP /* ia64 gets its own node_mem_map, before this, without bootmem */ if (!pgdat->node_mem_map) { - unsigned long size; + unsigned long size, start, end; struct page *map; - size = (pgdat->node_spanned_pages + 1) * sizeof(struct page); + /* + * The zone's endpoints aren't required to be MAX_ORDER + * aligned but the node_mem_map endpoints must be in order + * for the buddy allocator to function correctly. + */ + start = pgdat->node_start_pfn & ~(MAX_ORDER_NR_PAGES - 1); + end = pgdat->node_start_pfn + pgdat->node_spanned_pages; + end = ALIGN(end, MAX_ORDER_NR_PAGES); + size = (end - start) * sizeof(struct page); map = alloc_remap(pgdat->node_id, size); if (!map) map = alloc_bootmem_node(pgdat, size); - pgdat->node_mem_map = map; + pgdat->node_mem_map = map + (pgdat->node_start_pfn - start); } #ifdef CONFIG_FLATMEM /* _