I recompiled 2.6.8.1 with the option Enable kernel irq balancing disabled and so far the kernel has not Oops’d. I still get quite a few of these, though.

mlnet: page allocation failure. order:5, mode:0xd0

Perhaps I am back in business.

And yet, even with that option disabled, I still get plenty of allocation failures. I have even gotten a few from nfsd and cat at this point. I found a Usenet thread that provides some small insight, but no obvious resolution for my situation. This seems to be coming up in Google searches for 2.6.8.1, but not other variants. Perhaps I should try an earlier kernel in the 2.6 series.