d5a13901bf
By the time that pmap_init() runs, vm_phys_segs[] has been initialized. Obtaining the end of memory address from vm_phys_segs[] is a little easier than obtaining it from phys_avail[]. Enable the use of VM_PHYSSEG_SPARSE on amd64 and i386, making it the default on i386 PAE. (The use of VM_PHYSSEG_SPARSE on i386 PAE saves us some precious kernel virtual address space that would have been wasted on unused vm_page structures.)