[PATCH 1/2] Align the node_mem_map endpoints to a MAX_ORDER boundary

Mel Gorman
2006-05-19T13:43:01Z

From: Bob Picco <bob.picco@hp.com>

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.

include/linux/mmzone.h | 1 +
mm/page_alloc.c | 14 +++++++++++---
2 files changed, 12 insertions(+), 3 deletions(-)

Signed-off-by: Bob Picco <bob.picco@hp.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>

diff -rup -X /usr/src/patchset-0.5/bin//dontdiff linux-2.6.17-rc4-mm1-clean/include/linux/mmzone.h linux-2.6.17-rc4-mm1-101-bob-node-alignment/include/linux/mmzone.h
--- linux-2.6.17-rc4-mm1-clean/include/linux/mmzone.h 2006-05-18 17:23:55.000000000 +0100
+++ linux-2.6.17-rc4-mm1-101-bob-node-alignment/include/linux/mmzone.h 2006-05-18 17:52:13.000000000 +0100
@@ -21,6 +21,7 @@
#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 -rup -X /usr/src/patchset-0.5/bin//dontdiff linux-2.6.17-rc4-mm1-clean/mm/page_alloc.c linux-2.6.17-rc4-mm1-101-bob-node-alignment/mm/page_alloc.c
--- linux-2.6.17-rc4-mm1-clean/mm/page_alloc.c 2006-05-18 17:23:55.000000000 +0100
+++ linux-2.6.17-rc4-mm1-101-bob-node-alignment/mm/page_alloc.c 2006-05-18 17:58:10.000000000 +0100
@@ -2484,14 +2484,22 @@ 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
/*