Hi Mel !
Mel Gorman wrote:
> 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
[snip]
>
> 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)
>
ok for that part.
> #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;
is mem_map always aligned on MAX_ORDER ?
> #endif
> #endif /* CONFIG_FLAT_NODE_MEM_MAP */
> }
>
I'm not sure of that part. We basically make incoherent the use of
free_area_init_node()'s fourth parameter by doing this change (for
FLATMEM model of course).
When using free_area_init() which is defined as follow:
void __init free_area_init(unsigned long *zones_size)
{
free_area_init_node(0, NODE_DATA(0), zones_size,
__pa(PAGE_OFFSET) >> PAGE_SHIFT, NULL);
}
we will end up to have 2 definitions for the mem start:
- __pa(PAGE_OFFSET) >> PAGE_SHIFT
- ARCH_PFN_OFFSET
The former will be used to calculate the size of mem_map and the
latter will be used to calculate the offset between
NODE_DATA(0)->node_mem_map and PFN 0. I don't think that will result
in any problem since:
ARCH_PFN_OFFSET == __pa(PAGE_OFFSET) >> PAGE_SHIFT
That just makes the code is harder to follow.
But if some platforms were doing something like (which is unlikely)
[...]
free_area_init_node(0, NODE_DATA(0), zone_size, FOO_PFN_OFFSET, NULL);
[...]
and ARCH_PFN_OFFSET != FOO_PFN_OFFSET then they may have some troubles.
What about this patch for page_alloc.c ? I think it makes more obvious
what is ARCH_PFN_OFFSET. And if someone doesn't want to use
ARCH_PFN_OFFSET, he still can use:
free_area_init_node(0, NODE_DATA(0), zone_size, FOO_PFN_OFFSET, NULL);
Franck
-- >8 --
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 253a450..9daee06 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2147,7 +2147,7 @@ #ifdef CONFIG_FLATMEM
* With no DISCONTIG, the global mem_map is just set as node 0's
*/
if (pgdat == NODE_DATA(0))
- mem_map = NODE_DATA(0)->node_mem_map;
+ mem_map = NODE_DATA(0)->node_mem_map - pgdat->node_start_pfn;
#endif
#endif /* CONFIG_FLAT_NODE_MEM_MAP */
}
@@ -2172,10 +2172,13 @@ struct pglist_data contig_page_data = {
EXPORT_SYMBOL(contig_page_data);
#endif
+/*
+ * This function is used only by FLATMEM. In that case the
+ * start of physical mem is always given by ARCH_PFN_OFFSET.
+ */
void __init free_area_init(unsigned long *zones_size)
{
- free_area_init_node(0, NODE_DATA(0), zones_size,
- __pa(PAGE_OFFSET) >> PAGE_SHIFT, NULL);
+ free_area_init_node(0, NODE_DATA(0), zones_size, ARCH_PFN_OFFSET, NULL);
}
#ifdef CONFIG_PROC_FS
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
