Re: [BUG] 2.6.23-rc3-mm1 Kernel panic - not syncing: DMA: Memory

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 23 Aug 2007 10:22:26 -0700
"Luck, Tony" <tony.luck@intel.com> wrote:

> > __get_free_pages() of swiotlb_alloc_coherent() fails in rc3-mm1.
> > But, it doesn't fail on rc2-mm2, and kernel can boot up.
> 
> That looks to be part of the problem here ... failing an order=3
> allocation during boot on a system that just a few lines earlier
> in the boot log reported "Memory: 37474000k/37680640k available"
> looks bad ... but perhaps having *more* memory is part of your problem.
> You may have run low on GFP_DMA memory because some allocation
> scaled by memory size has chewed up a lot of your memory.  To check
> this try booting with a "mem=4G" parameter and see if that helps
> you.
> 
> But it is also bad that the swiotlb() code failed to handle this.
> Can you check whether the problem is related to the size of the
> allocation being just over 256K (a magic number for swiotlb since
> IO_TLB_SEGSIZE is 128 times a slab size of 2k).  Try changing
> lib/swiotlb.c to set IO_TLB_SEGSIZE to 256 instead.
> 

Others are reporting machines which fail int he memory allcoator much
earlier, and which claim to have four CPUs and 16 nodes.  So something is
very wonky in the rc3-mm1 page allocator.

I guess suspicion has to be directed at the memoryless-nodes patches, but
until that's cleared up I don't think there's much to be gained from
chasing this iommu problem, now that you've worked out that it's a bogus
memory allocation failure (thanks).