Index: sys/vm/swap_pager.c
===================================================================
--- sys/vm/swap_pager.c
+++ sys/vm/swap_pager.c
@@ -407,6 +407,7 @@
 static void	swp_sizecheck(void);
 static void	swp_pager_async_iodone(struct buf *bp);
 static bool	swp_pager_swblk_empty(struct swblk *sb, int start, int limit);
+static void	swp_pager_swblk_free_empty(vm_object_t, struct swblk *sb);
 static int	swapongeom(struct vnode *);
 static int	swaponvp(struct thread *, struct vnode *, u_long);
 static int	swapoff_one(struct swdevt *sp, struct ucred *cred);
@@ -424,6 +425,8 @@
 static void swp_pager_meta_free(vm_object_t, vm_pindex_t, vm_pindex_t);
 static void swp_pager_meta_free_all(vm_object_t);
 static daddr_t swp_pager_meta_ctl(vm_object_t, vm_pindex_t, int);
+static vm_pindex_t swp_pager_meta_find_least(vm_object_t, vm_pindex_t,
+    daddr_t*);
 
 static void
 swp_pager_init_freerange(daddr_t *start, daddr_t *num)
@@ -985,10 +988,13 @@
 	 * Transfer source to destination.
 	 */
 	swp_pager_init_freerange(&s_free, &n_free);
-	for (i = 0; i < dstobject->size; ++i) {
-		srcaddr = swp_pager_meta_ctl(srcobject, i + offset, SWM_POP);
-		if (srcaddr == SWAPBLK_NONE)
-			continue;
+
+	/*
+	 * Search srcobject pindex of corresponding dstobject between 0 and
+	 * dstobject->size to transfer.
+	 */
+	for (i = 0; (i = swp_pager_meta_find_least(srcobject, i + offset,
+	    &srcaddr) - offset) < dstobject->size; ++i) {
 		dstaddr = swp_pager_meta_ctl(dstobject, i, 0);
 		if (dstaddr != SWAPBLK_NONE) {
 			/*
@@ -1876,6 +1882,19 @@
 	}
 	return (true);
 }
+
+/*
+ * SWP_PAGER_SWBLK_FREE_EMPTY() - frees if a block is free
+ */
+static void
+swp_pager_swblk_free_empty(vm_object_t object, struct swblk *sb)
+{
+
+	if (swp_pager_swblk_empty(sb, 0, SWAP_META_PAGES)) {
+		SWAP_PCTRIE_REMOVE(&object->un_pager.swp.swp_blks, sb->p);
+		uma_zfree(swblk_zone, sb);
+	}
+}
    
 /*
  * SWP_PAGER_META_BUILD() -	add swap block to swap meta data for object
@@ -1994,11 +2013,8 @@
 	/*
 	 * Free the swblk if we end up with the empty page run.
 	 */
-	if (swapblk == SWAPBLK_NONE &&
-	    swp_pager_swblk_empty(sb, 0, SWAP_META_PAGES)) {
-		SWAP_PCTRIE_REMOVE(&object->un_pager.swp.swp_blks, rdpi);
-		uma_zfree(swblk_zone, sb);
-	}
+	if (swapblk == SWAPBLK_NONE)
+	    swp_pager_swblk_free_empty(object, sb);
 	return (prev_swapblk);
 }
 
@@ -2124,11 +2140,7 @@
 		return (SWAPBLK_NONE);
 	if ((flags & SWM_POP) != 0) {
 		sb->d[pindex % SWAP_META_PAGES] = SWAPBLK_NONE;
-		if (swp_pager_swblk_empty(sb, 0, SWAP_META_PAGES)) {
-			SWAP_PCTRIE_REMOVE(&object->un_pager.swp.swp_blks,
-			    rounddown(pindex, SWAP_META_PAGES));
-			uma_zfree(swblk_zone, sb);
-		}
+		swp_pager_swblk_free_empty(object, sb);
 	}
 	return (r1);
 }
@@ -2136,17 +2148,23 @@
 /*
  * Returns the least page index which is greater than or equal to the
  * parameter pindex and for which there is a swap block allocated.
+ * If removal argument is passed, the swpblk is removed.
  * Returns object's size if the object's type is not swap or if there
  * are no allocated swap blocks for the object after the requested
  * pindex.
  */
 vm_pindex_t
-swap_pager_find_least(vm_object_t object, vm_pindex_t pindex)
+swp_pager_meta_find_least(vm_object_t object, vm_pindex_t pindex,
+    daddr_t *removal)
 {
 	struct swblk *sb;
 	int i;
 
-	VM_OBJECT_ASSERT_LOCKED(object);
+	if (removal)
+		VM_OBJECT_ASSERT_WLOCKED(object);
+	else
+		VM_OBJECT_ASSERT_LOCKED(object);
+
 	if (object->type != OBJT_SWAP)
 		return (object->size);
 
@@ -2155,19 +2173,17 @@
 	if (sb == NULL)
 		return (object->size);
 	if (sb->p < pindex) {
-		for (i = pindex % SWAP_META_PAGES; i < SWAP_META_PAGES; i++) {
+		for (i = pindex % SWAP_META_PAGES; i < SWAP_META_PAGES; i++)
 			if (sb->d[i] != SWAPBLK_NONE)
-				return (sb->p + i);
-		}
+				goto found;
 		sb = SWAP_PCTRIE_LOOKUP_GE(&object->un_pager.swp.swp_blks,
 		    roundup(pindex, SWAP_META_PAGES));
 		if (sb == NULL)
 			return (object->size);
 	}
-	for (i = 0; i < SWAP_META_PAGES; i++) {
+	for (i = 0; i < SWAP_META_PAGES; i++)
 		if (sb->d[i] != SWAPBLK_NONE)
-			return (sb->p + i);
-	}
+			goto found;
 
 	/*
 	 * We get here if a swblk is present in the trie but it
@@ -2175,6 +2191,27 @@
 	 */
 	MPASS(0);
 	return (object->size);
+found:
+	if (removal) {
+		*removal = sb->d[pindex % SWAP_META_PAGES];
+		sb->d[pindex % SWAP_META_PAGES] = SWAPBLK_NONE;
+		swp_pager_swblk_free_empty(object, sb);
+	}
+	return (sb->p + i);
+}
+
+/*
+ * Returns the least page index which is greater than or equal to the
+ * parameter pindex and for which there is a swap block allocated.
+ * Returns object's size if the object's type is not swap or if there
+ * are no allocated swap blocks for the object after the requested
+ * pindex.
+ */
+vm_pindex_t
+swap_pager_find_least(vm_object_t object, vm_pindex_t pindex)
+{
+
+	return swp_pager_meta_find_least(object, pindex, NULL);
 }
 
 /*