At some point someone decided to use extent maps to keep track of swap
   space.



FWIW, this change occured when i rewrote vm_swap.c, well before even UVM.


revision 1.38
date: 1997/06/12 14:51:20;  author: mrg;  state: Exp;  lines: +1025 -371
bring mrg-vm-swap2 onto mainilne.



.mrg.