pmap_pv_alloc
newpv = pmap_pv_alloc();
if (!pve && !(pve = pmap_pv_alloc())) {
static inline struct pv_entry *pmap_pv_alloc(void);
pve = pmap_pv_alloc();
newpv = pmap_pv_alloc(true/*nowait flag*/);
newpv = pmap_pv_alloc(false/*nowait flag*/);
apv = (pv_entry_t)pmap_pv_alloc();