Re: [PATCH] gurantee DMA area for alloc_bootmem_low() ver. 2.

Andi Kleen
2005-08-18T21:39:27Z

Andrew Morton <akpm@osdl.org> writes:
> >
> > To avoid this panic, following patch confirm allocated area, and retry
> > if it is not in DMA.
> > I tested this patch on my Tiger 4 and our new server.
>
> It kills my x86_64 box:

Funny I ran into a similar problem recently. On a multi node x86-64
system when swiotlb is forced (normally those are AMD systems which
use the AMD hardware IOMMU) the bootmem_alloc in swiotlb.c would
allocate from the last node. Why? Because alloc_bootmem just
does for_each_pgdat() and tries each node and the pgdat list
starts with the highest node going down to the lowest.

I just changed the ordering of the pgdat list that made bootmem
work again.

-Andi

Index: linux/mm/bootmem.c
===================================================================
--- linux.orig/mm/bootmem.c
+++ linux/mm/bootmem.c
@@ -61,9 +61,17 @@ static unsigned long __init init_bootmem
{
bootmem_data_t *bdata = pgdat->bdata;
unsigned long mapsize = ((end - start)+7)/8;
+ static struct pglist_data *pgdat_last;

- pgdat->pgdat_next = pgdat_list;
- pgdat_list = pgdat;
+ pgdat->pgdat_next = NULL;
+ /* Add new nodes last so that bootmem always starts
+ searching in the first nodes, not the last ones */
+ if (pgdat_last)
+ pgdat_last->pgdat_next = pgdat;
+ else {
+ pgdat_list = pgdat;
+ pgdat_last = pgdat;
+ }

mapsize = ALIGN(mapsize, sizeof(long));
bdata->node_bootmem_map = phys_to_virt(mapstart << PAGE_SHIFT);