Function vm_page_wire_mapped

freebsd/vm/vm_page.c:3931–3950

* Attempt to wire a mapped page following a pmap lookup of that page. * This may fail if a thread is concurrently tearing down mappings of the page. * The transient failure is acceptable because it translates to the * failure of the caller pmap_extract_and_hold(), which should be then * followed by the vm_fault() fallback, see e.g. vm_fault_quick_hold_pages(). */

 * followed by the vm_fault() fallback, see e.g. vm_fault_quick_hold_pages().
 */
bool
vm_page_wire_mapped(vm_page_t m)
{
	u_int old;

	old = m->ref_count;
	do {
		KASSERT(old > 0,
		    ("vm_page_wire_mapped: wiring unreferenced page %p", m));
		if ((old & VPRC_BLOCKED) != 0)
			return (false);
	} while (!atomic_fcmpset_int(&m->ref_count, &old, old + 1));

	if (VPRC_WIRE_COUNT(old) == 0) {
		if ((m->oflags & VPO_UNMANAGED) == 0)
			vm_page_aflag_set(m, PGA_DEQUEUE);
		vm_wire_add(1);
	}
	return (true);
}

/*
 * Release a wiring reference to a managed page.  If the page still belongs to