Dave Hansen wrote: [Thu May 04 2006, 11:21:06AM EDT]
> I haven't thought through it completely, but these two lines worry me:
>
> > + start = pgdat->node_start_pfn & ~((1 << (MAX_ORDER - 1)) - 1);
> > + end = start + pgdat->node_spanned_pages;
>
> Should the "end" be based off of the original "start", or the aligned
> "start"?
Yes. I failed to quilt refresh before sending. You mean end should be
end = pgdat->node_start_pfn + pgdat->node_spanned_pages before rounding
up.
>
> (using decimal math to make it easy) ...
>
> Let's say that MAX_ORDER comes out to be 10 pages. node_start_pfn is 9,
> and the node's end pfn is 21. node_spanned_pages will be 12. "start"
> will get rounded down to 0. "end" will be "start" (0) +
> node_spanned_pages (12), so 12. "end" then gets rounded up to 20.
> However, this is not sufficient space for the mem_map as the node
> *actually* ended at 21.
>
> I think that "end" needs to be calculated without rounding down the
> start_pfn, or the node_spanned_pages number needs to be rounded up in
> the same way that "end" is.
>
> Does that sound right?
Yes.
>
> Also, it might look nicer if there was an intermediate variable
> something like this:
>
> #define MAX_ORDER_NR_PAGES (1 << (MAX_ORDER - 1))
Yes.
>
> Take a look at the loop below, I've also used ALIGN() from kernel.h for
> the "end" alignment. I think it is just a drop-in replacement.
>
> /* ia64 gets its own node_mem_map, before this, without bootmem */
> if (!pgdat->node_mem_map) {
> unsigned long size, start, end;
> struct page *map;
>
> /*
> * 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 = start + 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_start_pfn - start);
> }
>
> -- Dave
bob
>
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