Keep in mind process_madvise() is not limited by IOV_MAX, which can be rather
high, but rather UIO_FASTIOV, which is limited to 8 entries.
(Some have been surprised by this limitation...!)
So I think at this point scaling isn't a huge issue, I raise it because in
future we may want to increase this limit, at which point we should think about
it, which is why I sort of hand-waved it away a bit.