Index: sys/vm/swap_pager.c
===================================================================
--- sys/vm/swap_pager.c
+++ sys/vm/swap_pager.c
@@ -985,7 +985,18 @@
 	 * Transfer source to destination.
 	 */
 	swp_pager_init_freerange(&s_free, &n_free);
-	for (i = 0; i < dstobject->size; ++i) {
+
+	/*
+	 * Search srcobject pindex of corresponding dstobject between 0 and
+	 * dstobject->size to transfer.
+	 *
+	 * Based on experiments, about 80% to 95% of vm_indexes are
+	 * SWAPBLK_NONE.  Calling swap_pager_find_least() adds extra
+	 * pctrie lookups.  However, skipping SWAPBLK_NONE gives us saving
+	 * of pctrie lookups in total.
+	 */
+	for (i = 0; (i = swap_pager_find_least(srcobject, i + offset) - offset)
+	        < dstobject->size; ++i) {
 		srcaddr = swp_pager_meta_ctl(srcobject, i + offset, SWM_POP);
 		if (srcaddr == SWAPBLK_NONE)
 			continue;