Function vm_page_unwire_managed

freebsd/vm/vm_page.c:3957–4003

* Release a wiring reference to a managed page. If the page still belongs to * an object, update its position in the page queues to reflect the reference. * If the wiring was the last reference to the page, free the page. */

 * If the wiring was the last reference to the page, free the page.
 */
static void
vm_page_unwire_managed(vm_page_t m, uint8_t nqueue, bool noreuse)
{
	u_int old;

	KASSERT((m->oflags & VPO_UNMANAGED) == 0,
	    ("%s: page %p is unmanaged", __func__, m));

	/*
	 * Update LRU state before releasing the wiring reference.
	 * Use a release store when updating the reference count to
	 * synchronize with vm_page_free_prep().
	 */
	old = m->ref_count;
	do {
		KASSERT(VPRC_WIRE_COUNT(old) > 0,
		    ("vm_page_unwire: wire count underflow for page %p", m));

		if (old > VPRC_OBJREF + 1) {
			/*
			 * The page has at least one other wiring reference.  An
			 * earlier iteration of this loop may have called
			 * vm_page_release_toq() and cleared PGA_DEQUEUE, so
			 * re-set it if necessary.
			 */
			if ((vm_page_astate_load(m).flags & PGA_DEQUEUE) == 0)
				vm_page_aflag_set(m, PGA_DEQUEUE);
		} else if (old == VPRC_OBJREF + 1) {
			/*
			 * This is the last wiring.  Clear PGA_DEQUEUE and
			 * update the page's queue state to reflect the
			 * reference.  If the page does not belong to an object
			 * (i.e., the VPRC_OBJREF bit is clear), we only need to
			 * clear leftover queue state.
			 */
			vm_page_release_toq(m, nqueue, noreuse);
		} else if (old == 1) {
			vm_page_aflag_clear(m, PGA_DEQUEUE);
		}
	} while (!atomic_fcmpset_rel_int(&m->ref_count, &old, old - 1));

	if (VPRC_WIRE_COUNT(old) == 1) {
		vm_wire_sub(1);
		if (old == 1)
			vm_page_free(m);
	}
}

/*
 * Release one wiring of the specified page, potentially allowing it to be