Function vm_pageout_launder

freebsd/vm/vm_pageout.c:721–960

* Attempt to launder the specified number of pages. * * Returns the number of pages successfully laundered. */

 * Returns the number of pages successfully laundered.
 */
static int
vm_pageout_launder(struct vm_domain *vmd, int launder, bool in_shortfall)
{
	struct scan_state ss;
	struct vm_pagequeue *pq;
	vm_object_t object;
	vm_page_t m, marker;
	vm_page_astate_t new, old;
	int act_delta, error, numpagedout, queue, refs, starting_target;
	int vnodes_skipped;
	bool pageout_ok;

	object = NULL;
	starting_target = launder;
	vnodes_skipped = 0;

	/*
	 * Scan the laundry queues for pages eligible to be laundered.  We stop
	 * once the target number of dirty pages have been laundered, or once
	 * we've reached the end of the queue.  A single iteration of this loop
	 * may cause more than one page to be laundered because of clustering.
	 *
	 * As an optimization, we avoid laundering from PQ_UNSWAPPABLE when no
	 * swap devices are configured.
	 */
	if (atomic_load_acq_int(&swapdev_enabled))
		queue = PQ_UNSWAPPABLE;
	else
		queue = PQ_LAUNDRY;

scan:
	marker = &vmd->vmd_markers[queue];
	pq = &vmd->vmd_pagequeues[queue];
	vm_pagequeue_lock(pq);
	vm_pageout_init_scan(&ss, pq, marker, NULL, pq->pq_cnt);
	while (launder > 0 && (m = vm_pageout_next(&ss, false)) != NULL) {
		if (__predict_false((m->flags & PG_MARKER) != 0))
			continue;

		/*
		 * Don't touch a page that was removed from the queue after the
		 * page queue lock was released.  Otherwise, ensure that any
		 * pending queue operations, such as dequeues for wired pages,
		 * are handled.
		 */
		if (vm_pageout_defer(m, queue, true))
			continue;

		/*
		 * Lock the page's object.
		 */
		if (object == NULL || object != m->object) {
			if (object != NULL)
				VM_OBJECT_WUNLOCK(object);
			object = atomic_load_ptr(&m->object);
			if (__predict_false(object == NULL))
				/* The page is being freed by another thread. */
				continue;