Re: assert/crash in __rmqueue() when enabling CONFIG_NUMA

["Bob Picco" <bob.picco@hp.com>]

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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