The FLATMEM memory model assumes that memory is one contiguous region based
at PFN 0 and uses the NODE_DATA(0)->node_mem_map as the global mem_map. As
NODE_DATA(0)->node_mem_map may not be PFN 0, architectures optionally define
ARCH_PFN_OFFSET as the offset between NODE_DATA(0)->node_mem_map and PFN 0.
This offset is used every time page_to_pfn() or pfn_to_page() is called
resulting in a small amount of code bloat and overhead.
This patch changes ARCH_PFN_OFFSET so that it is used only once during
memory initialisation when working out where mem_map is. This gives
a very small reduction in zImage size for architectures using
ARCH_PFN_OFFSET. The patch also adds a small amount of documentation
on what ARCH_PFN_OFFSET is for.
Signed-off-by: Mel Gorman <[email protected]>
include/asm-generic/memory_model.h | 5 ++---
mm/page_alloc.c | 8 ++++++--
2 files changed, 8 insertions(+), 5 deletions(-)
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.17-mm6-clean/include/asm-generic/memory_model.h linux-2.6.17-mm6-archpfnoffset_optimise/include/asm-generic/memory_model.h
--- linux-2.6.17-mm6-clean/include/asm-generic/memory_model.h 2006-07-05 14:31:17.000000000 +0100
+++ linux-2.6.17-mm6-archpfnoffset_optimise/include/asm-generic/memory_model.h 2006-07-05 14:36:04.000000000 +0100
@@ -28,9 +28,8 @@
*/
#if defined(CONFIG_FLATMEM)
-#define __pfn_to_page(pfn) (mem_map + ((pfn) - ARCH_PFN_OFFSET))
-#define __page_to_pfn(page) ((unsigned long)((page) - mem_map) + \
- ARCH_PFN_OFFSET)
+#define __pfn_to_page(pfn) (mem_map + (pfn))
+#define __page_to_pfn(page) ((unsigned long)((page) - mem_map))
#elif defined(CONFIG_DISCONTIGMEM)
#define __pfn_to_page(pfn) \
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.17-mm6-clean/mm/page_alloc.c linux-2.6.17-mm6-archpfnoffset_optimise/mm/page_alloc.c
--- linux-2.6.17-mm6-clean/mm/page_alloc.c 2006-07-05 14:31:18.000000000 +0100
+++ linux-2.6.17-mm6-archpfnoffset_optimise/mm/page_alloc.c 2006-07-05 17:01:01.000000000 +0100
@@ -2157,10 +2157,14 @@ static void __init alloc_node_mem_map(st
}
#ifdef CONFIG_FLATMEM
/*
- * With no DISCONTIG, the global mem_map is just set as node 0's
+ * With FLATMEM, the global mem_map is just set as node 0's. The
+ * FLATMEM memory model assumes that memory is in one contiguous area
+ * starting at PFN 0. Architectures that do not start NODE 0 at PFN 0
+ * must define ARCH_PFN_OFFSET as the offset between
+ * NODE_DATA(0)->node_mem_map and PFN 0.
*/
if (pgdat == NODE_DATA(0))
- mem_map = NODE_DATA(0)->node_mem_map;
+ mem_map = NODE_DATA(0)->node_mem_map - ARCH_PFN_OFFSET;
#endif
#endif /* CONFIG_FLAT_NODE_MEM_MAP */
}
-
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