Function vm_object_deallocate

freebsd/vm/vm_object.c:617–690

* vm_object_deallocate: * * Release a reference to the specified object, * gained either through a vm_object_allocate * or a vm_object_reference call. When all references * are gone, storage associated with this object * may be relinquished. * * No object may be locked. */

 *	No object may be locked.
 */
void
vm_object_deallocate(vm_object_t object)
{
	vm_object_t temp;
	bool released;

	while (object != NULL) {
		/*
		 * If the reference count goes to 0 we start calling
		 * vm_object_terminate() on the object chain.  A ref count
		 * of 1 may be a special case depending on the shadow count
		 * being 0 or 1.  These cases require a write lock on the
		 * object.
		 */
		if ((object->flags & OBJ_ANON) == 0)
			released = refcount_release_if_gt(&object->ref_count, 1);
		else
			released = refcount_release_if_gt(&object->ref_count, 2);
		if (released)
			return;

		if (object->type == OBJT_VNODE) {
			VM_OBJECT_RLOCK(object);
			if (object->type == OBJT_VNODE) {
				vm_object_deallocate_vnode(object);
				return;
			}
			VM_OBJECT_RUNLOCK(object);
		}

		VM_OBJECT_WLOCK(object);
		KASSERT(object->ref_count > 0,
		    ("vm_object_deallocate: object deallocated too many times: %d",
		    object->type));

		/*
		 * If this is not the final reference to an anonymous
		 * object we may need to collapse the shadow chain.
		 */
		if (!refcount_release(&object->ref_count)) {
			if (object->ref_count > 1 ||
			    object->shadow_count == 0) {
				if ((object->flags & OBJ_ANON) != 0 &&
				    object->ref_count == 1)
					vm_object_set_flag(object,
					    OBJ_ONEMAPPING);
				VM_OBJECT_WUNLOCK(object);
				return;
			}

			/* Handle collapsing last ref on anonymous objects. */
			object = vm_object_deallocate_anon(object);
			continue;
		}

		/*
		 * Handle the final reference to an object.  We restart
		 * the loop with the backing object to avoid recursion.