This is a little tricky, since we only know we want hugetlbfs after memory
has been initialized, so we start up in anonymous memory, and later
switch to hugetlbfs by copying it to hugetlb-backed memory and mremap()ing
it back into place.
Allow memory users to declare methods of reclaiming memory (reclaimers),
and allow the main loop to declare a safe point for calling these reclaimers.
The memory mananger will then schedule calls to reclaimers when memory runs
low.
