The pmap_change_wiring function changes the wiring attribute for the page at virtual address va in the physical map pmap. A wired page gets its name from being "wired" into the system page tables so that it will not be paged out.
The mapping must already exist in the pmap. If wired is TRUE, the maps wired page count will be incremented; if FALSE, it will be decremented.
It is typically called by the vm_fault_unwire function.