> 
> I believe FreeBSD also solves this problem, but i don't know how.
> Perhaps somebody who's familiar with their code could comment.
> 

FreeBSD allocates 252MB for kernel space.  Not all of the
page table pages are allocated initially, but as space
is allocated from the kernel map, page table pages are
added.  The FreeBSD scheme is totally dynamic up to
the 252MB limit.  The limit itself is compile-time
tunable.  On FreeBSD there is NO wastage of kernel
page table pages by having to make a liberal guess
at the number of kernel page table pages needed.

John
dyson@freebsd.org