the attached highmem-2.3.30-B4 patch (against 2.3.30-pre5) fixes the bug
noticed by Stephen: PAE mode must always use atomic 64-bit stores to
update page table entries, otherwise TLBs might get corrupted. (we do not
use atomic load-modify-stores because access to pagetables is serialized
by the pagetable spinlock.)

this actually was a bit more complex because a number of places within the
x86 architecture modified ptes directly.

with this patch the 64GB kernel runs very stable under high load. (2-level
page table kernels compile cleanly/boot/work as well)

-- mingo