On Mon, 26 Jun 2006, Franck Bui-Huu wrote:
Hi Mel
Mel Gorman wrote:
On Fri, 23 Jun 2006, Franck Bui-Huu wrote:
[snip]
-unsigned long __init init_bootmem (unsigned long start, unsigned long
pages)
+unsigned long __init init_bootmem(unsigned long start, unsigned long
pages)
{
max_low_pfn = pages;
min_low_pfn = start;
- return(init_bootmem_core(NODE_DATA(0), start, 0, pages));
+ return init_bootmem_core(NODE_DATA(0), start, ARCH_PFN_OFFSET,
pages);
}
Not all arches will use init_bootmem(). Arm for example uses
init_bootmem_node(). ARCH_PFN_OFFSET is only meant to affect mem_map,
well, I don't agree here. ARCH_PFN_OFFSET is used to save the first
page number that has physical memory. I don't see why we couldn't use
it to correctly initialise the memory system...
Architectures will not always have a known fixed start of physical memory.
On IA64 at least, they initialise memory as if it starts at 0 but on my
one test machine, the beginning part is always a memory hole. I've seen
nothing to indicate that this hole will be the same size on all IA64
machines but I kinda doubt it. Also, arches that use init_bootmem() do not
necessary use free_area_init().
If we don't change init_bootmem() to use ARCH_PFN_OFFSET, then the
kernel will initialise the start of memory to 0 which is boggus.
IOW,
we can't use this function without this change (except if your memory
start at 0 of course). And I think that init_bootmem() has been
implemented for systems which have only one node _whatever_ memory
start value...
While you may be right, it'll only fix the problem for arches with
ARCH_PFN_OFFSET and using init_bootmem (which is the case of MIPS I
guess). But arches using init_bootmem_node or not using free_area_init()
may still get kicked.
#ifndef CONFIG_HAVE_ARCH_BOOTMEM_NODE
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
[snip]
@@ -2174,8 +2181,7 @@ #endif
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);
}
Same comment applies as for init_bootmem(). I can't be sure it's a good
idea.
same comment as for init_bootmem()
Franck
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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