Function pmap_allocpte_alloc

freebsd/amd64/amd64/pmap.c:4526–4541

* This routine is called if the desired page table page does not exist. * * If page table page allocation fails, this routine may sleep before * returning NULL. It sleeps only if a lock pointer was given. Sleep * occurs right before returning to the caller. This way, we never * drop pmap lock to sleep while a page table page has ref_count == 0, * which prevents the page from being freed un

 * which prevents the page from being freed under us.
 */
static vm_page_t
pmap_allocpte_alloc(pmap_t pmap, vm_pindex_t ptepindex, struct rwlock **lockp,
    vm_offset_t va)
{
	vm_page_t m;

	m = pmap_allocpte_nosleep(pmap, ptepindex, lockp, va);
	if (m == NULL && lockp != NULL) {
		RELEASE_PV_LIST_LOCK(lockp);
		PMAP_UNLOCK(pmap);
		PMAP_ASSERT_NOT_IN_DI();
		vm_wait(NULL);
		PMAP_LOCK(pmap);
	}
	return (m);
}

static pd_entry_t *
pmap_alloc_pde(pmap_t pmap, vm_offset_t va, vm_page_t *pdpgp,