Index: sys/kern/subr_pctrie.c
===================================================================
--- sys/kern/subr_pctrie.c
+++ sys/kern/subr_pctrie.c
@@ -738,42 +738,25 @@
 }
 #endif
 
-/*
- * Remove the specified index from the tree, and return the value stored at
- * that index.  If the index is not present, return NULL.
- */
-uint64_t *
-pctrie_remove_lookup(struct pctrie *ptree, uint64_t index,
-    struct pctrie_node **freenode)
+static void
+pctrie_remove(struct pctrie *ptree, uint64_t index, struct pctrie_node *parent,
+    struct pctrie_node *node, struct pctrie_node **freenode)
 {
-	struct pctrie_node *child, *node, *parent;
-	uint64_t *m;
+	struct pctrie_node *child;
 	int slot;
 
-	*freenode = node = NULL;
-	child = pctrie_root_load(ptree, NULL, PCTRIE_LOCKED);
-	for (;;) {
-		if (pctrie_isleaf(child))
-			break;
-		parent = node;
-		node = child;
-		slot = pctrie_slot(node, index);
-		child = pctrie_node_load(&node->pn_child[slot], NULL,
-		    PCTRIE_LOCKED);
-	}
-	if ((m = pctrie_toval(child)) == NULL || *m != index)
-		return (NULL);
 	if (node == NULL) {
 		pctrie_root_store(ptree, PCTRIE_NULL, PCTRIE_LOCKED);
-		return (m);
+		return;
 	}
+	slot = pctrie_slot(node, index);
 	KASSERT((node->pn_popmap & (1 << slot)) != 0,
 	    ("%s: bad popmap slot %d in node %p",
 	    __func__, slot, node));
 	node->pn_popmap ^= 1 << slot;
 	pctrie_node_store(&node->pn_child[slot], PCTRIE_NULL, PCTRIE_LOCKED);
 	if (!powerof2(node->pn_popmap))
-		return (m);
+		return;
 	KASSERT(node->pn_popmap != 0, ("%s: bad popmap all zeroes", __func__));
 	slot = ffs(node->pn_popmap) - 1;
 	child = pctrie_node_load(&node->pn_child[slot], NULL, PCTRIE_LOCKED);
@@ -795,6 +778,34 @@
 	 */
 	pctrie_node_put(node);
 	*freenode = node;
+}
+
+/*
+ * Remove the specified index from the tree, and return the value stored at
+ * that index.  If the index is not present, return NULL.
+ */
+uint64_t *
+pctrie_remove_lookup(struct pctrie *ptree, uint64_t index,
+    struct pctrie_node **freenode)
+{
+	struct pctrie_node *child, *node, *parent;
+	uint64_t *m;
+	int slot;
+
+	*freenode = node = NULL;
+	child = pctrie_root_load(ptree, NULL, PCTRIE_LOCKED);
+	for (;;) {
+		if (pctrie_isleaf(child))
+			break;
+		parent = node;
+		node = child;
+		slot = pctrie_slot(node, index);
+		child = pctrie_node_load(&node->pn_child[slot], NULL,
+		    PCTRIE_LOCKED);
+	}
+	if ((m = pctrie_toval(child)) == NULL || *m != index)
+		return (NULL);
+	pctrie_remove(ptree, index, parent, node, freenode);
 	return (m);
 }
 
@@ -901,6 +912,126 @@
 	    callback, keyoff, arg));
 }
 
+/*
+ * Find first leaf >= index, and fill iter with the path to the parent of that
+ * leaf.
+ */
+static uint64_t *
+pctrie_iter_index(struct pctrie_iter *iter, struct pctrie_node *node,
+    uint64_t index)
+{
+	uint64_t *m;
+	int slot;
+
+	/* Seek a node that matches index. */
+	while (!pctrie_isleaf(node) &&
+	       !pctrie_keybarr(node, index, &slot)) {
+		iter->path[iter->top++] = node;
+		node = pctrie_node_load(&node->pn_child[slot], NULL,
+		    PCTRIE_LOCKED);
+	}
+
+	/*
+	 * If no such node was found, and instead this path leads only to nodes
+	 * < index, back up to find a subtrie with the least value > index.
+	 */
+	if (pctrie_isleaf(node) ?
+	    (m = pctrie_toval(node)) == NULL || *m < index :
+	    node->pn_owner < index) {
+		/* Climb the path to find a node with a descendant > index. */
+		do {
+			if (iter->top == 0)
+				return (NULL);
+			node = iter->path[--iter->top];
+			slot = pctrie_slot(node, index) + 1;
+		} while ((node->pn_popmap >> slot) == 0);
+
+		/* Step to the least child with a descendant > index. */
+		slot += ffs(node->pn_popmap >> slot) - 1;
+		iter->top++;
+		node = pctrie_node_load(&node->pn_child[slot], NULL,
+		    PCTRIE_LOCKED);
+	}
+	/* Descend to the least leaf of the subtrie. */
+	while (!pctrie_isleaf(node)) {
+		slot = ffs(node->pn_popmap) - 1;
+		iter->path[iter->top++] = node;
+		node = pctrie_node_load(&node->pn_child[slot], NULL,
+		    PCTRIE_LOCKED);
+	}
+	m = pctrie_toval(node);
+	iter->index = *m;
+	return (m);
+}
+
+/*
+ * Find the first leaf with value at least 'step' greater than the previous
+ * leaf.
+ */
+uint64_t *
+pctrie_iter_step(struct pctrie_iter *iter, uint64_t step)
+{
+	struct pctrie_node *node;
+	uint64_t index = iter->index + step;
+	int slot;
+
+	/* If the root */
+	if (iter->top == 0) {
+		uint64_t *m;
+		node = pctrie_root_load(iter->ptree, NULL, PCTRIE_UNSERIALIZED);
+		if (node != NULL && *(m = pctrie_toval(node)) >= index) {
+			iter->index = *m;
+			return (m);
+		}
+	}
+
+	/* Climb the path to find a node that matches a prefix of index. */
+	do {
+		if (iter->top == 0)
+			return (NULL);
+		node = iter->path[--iter->top];
+	} while (pctrie_keybarr(node, index, &slot));
+
+	/* Complete the search for index from node. */
+	iter->top++;
+	node = pctrie_node_load(&node->pn_child[slot], NULL, PCTRIE_LOCKED);
+	return (pctrie_iter_index(iter, node, index));
+}
+
+/*
+ * Find first leaf >= index, and initialize iter with the path to the parent of
+ * that leaf.
+ */
+uint64_t *
+pctrie_iter_start(struct pctrie_iter *iter,
+    struct pctrie *ptree, uint64_t index)
+{
+	struct pctrie_node *node = pctrie_root_load(ptree, NULL, PCTRIE_LOCKED);
+
+	iter->ptree = ptree;
+	iter->top = 0;
+	return (pctrie_iter_index(iter, node, index));
+}
+
+/*
+ * Remove from the trie the leaf last chosen by the iterator, and
+ * adjust the path if it's last member is to be freed.
+ */
+void
+pctrie_iter_remove(struct pctrie_iter *iter, struct pctrie_node **freenode)
+{
+	struct pctrie_node *node = NULL, *parent = NULL;
+
+	if (iter->top >= 1)
+		node = iter->path[iter->top - 1];
+	if (iter->top >= 2)
+		parent = iter->path[iter->top - 2];
+	*freenode = NULL;
+	pctrie_remove(iter->ptree, iter->index, parent, node, freenode);
+	if (*freenode != NULL)
+		--iter->top;
+}
+
 /*
  * Replace an existing value in the trie with another one.
  * Panics if there is not an old value in the trie at the new value's index.
Index: sys/kern/subr_rangeset.c
===================================================================
--- sys/kern/subr_rangeset.c
+++ sys/kern/subr_rangeset.c
@@ -272,8 +272,8 @@
 int
 rangeset_copy(struct rangeset *dst_rs, struct rangeset *src_rs)
 {
+	struct pctrie_iter iter;
 	struct rs_el *src_r, *dst_r;
-	uint64_t cursor;
 	int error;
 
 	MPASS(pctrie_is_empty(&dst_rs->rs_trie));
@@ -281,10 +281,8 @@
 	MPASS(dst_rs->rs_dup_data == src_rs->rs_dup_data);
 
 	error = 0;
-	for (cursor = 0;; cursor = src_r->re_start + 1) {
-		src_r = RANGESET_PCTRIE_LOOKUP_GE(&src_rs->rs_trie, cursor);
-		if (src_r == NULL)
-			break;
+	for (src_r = RANGESET_PCTRIE_ITER_START(&iter, &src_rs->rs_trie, 0);
+	     src_r != NULL; src_r = RANGESET_PCTRIE_ITER_STEP(&iter, 1)) {
 		dst_r = dst_rs->rs_dup_data(dst_rs->rs_data_ctx, src_r);
 		if (dst_r == NULL) {
 			error = ENOMEM;
@@ -303,13 +301,11 @@
 static void
 rangeset_check(struct rangeset *rs)
 {
+	struct pctrie_iter iter;
 	struct rs_el *r, *rp;
-	uint64_t cursor;
 
-	for (cursor = 0, rp = NULL;; cursor = r->re_start + 1, rp = r) {
-		r = RANGESET_PCTRIE_LOOKUP_GE(&rs->rs_trie, cursor);
-		if (r == NULL)
-			break;
+	for (rp = NULL, r = RANGESET_PCTRIE_ITER_START(&iter, &rs->rs_trie, 0);
+	     r != NULL; rp = r, r = RANGESET_PCTRIE_ITER_STEP(&iter, 1)) {
 		KASSERT(r->re_start < r->re_end,
 		    ("invalid interval rs %p elem %p (%#jx, %#jx)",
 		    rs, r, (uintmax_t)r->re_start,  (uintmax_t)r->re_end));
@@ -332,9 +328,9 @@
 
 DB_SHOW_COMMAND(rangeset, rangeset_show_fn)
 {
+	struct pctrie_iter iter;
 	struct rangeset *rs;
 	struct rs_el *r;
-	uint64_t cursor;
 
 	if (!have_addr) {
 		db_printf("show rangeset addr\n");
@@ -343,10 +339,8 @@
 
 	rs = (struct rangeset *)addr;
 	db_printf("rangeset %p\n", rs);
-	for (cursor = 0;; cursor = r->re_start + 1) {
-		r = RANGESET_PCTRIE_LOOKUP_GE(&rs->rs_trie, cursor);
-		if (r == NULL)
-			break;
+	for (r = RANGESET_PCTRIE_ITER_START(&iter, &rs->rs_trie, 0);
+	     r != NULL; r = RANGESET_PCTRIE_ITER_STEP(&iter, 1)) {
 		db_printf("  el %p start %#jx end %#jx\n",
 		    r, r->re_start, r->re_end);
 	}
Index: sys/sys/pctrie.h
===================================================================
--- sys/sys/pctrie.h
+++ sys/sys/pctrie.h
@@ -240,6 +240,31 @@
 }									\
 									\
 static __inline __unused struct type *					\
+name##_PCTRIE_ITER_STEP(struct pctrie_iter *iter, int64_t step)		\
+{									\
+	return name##_PCTRIE_VAL2PTR(					\
+		pctrie_iter_step(iter, step));				\
+}									\
+									\
+static __inline __unused struct type *					\
+name##_PCTRIE_ITER_START(struct pctrie_iter *iter,			\
+			struct pctrie *ptree, int64_t index)		\
+{									\
+	return name##_PCTRIE_VAL2PTR(					\
+	    pctrie_iter_start(iter, ptree, index));			\
+}									\
+									\
+static __inline __unused void						\
+name##_PCTRIE_ITER_REMOVE(struct pctrie_iter *iter)			\
+{									\
+	struct pctrie_node *freenode;					\
+									\
+	pctrie_iter_remove(iter, &freenode);				\
+	if (freenode != NULL)						\
+		freefn(iter->ptree, freenode);				\
+}									\
+									\
+static __inline __unused struct type *					\
 name##_PCTRIE_REPLACE(struct pctrie *ptree, struct type *ptr)		\
 {									\
 									\
@@ -295,6 +320,12 @@
 		    pctrie_cb_t callback, int keyoff, void *arg);
 struct pctrie_node *pctrie_reclaim_resume_cb(struct pctrie_node **pnode,
 		    pctrie_cb_t callback, int keyoff, void *arg);
+struct pctrie_iter;
+uint64_t	*pctrie_iter_step(struct pctrie_iter *iter, uint64_t step);
+uint64_t	*pctrie_iter_start(struct pctrie_iter *iter,
+		    struct pctrie *ptree, uint64_t index);
+void		pctrie_iter_remove(struct pctrie_iter *iter,
+		    struct pctrie_node **freenode);
 uint64_t	*pctrie_remove_lookup(struct pctrie *ptree, uint64_t index,
 		    struct pctrie_node **killnode);
 uint64_t	*pctrie_replace(struct pctrie *ptree, uint64_t *newval);
@@ -343,5 +374,12 @@
 
 #define	PCTRIE_COUNT	(1 << PCTRIE_WIDTH)
 
+struct pctrie_iter {
+	struct pctrie_node *path[sizeof(uint64_t) * NBBY / PCTRIE_WIDTH];
+	struct pctrie *ptree;
+	uint64_t index;
+	int top;
+};
+
 #endif /* _KERNEL */
 #endif /* !_SYS_PCTRIE_H_ */
Index: sys/vm/swap_pager.c
===================================================================
--- sys/vm/swap_pager.c
+++ sys/vm/swap_pager.c
@@ -1797,8 +1797,8 @@
 u_long
 swap_pager_swapped_pages(vm_object_t object)
 {
+	struct pctrie_iter iter;
 	struct swblk *sb;
-	vm_pindex_t pi;
 	u_long res;
 	int i;
 
@@ -1807,9 +1807,10 @@
 	if (pctrie_is_empty(&object->un_pager.swp.swp_blks))
 		return (0);
 
-	for (res = 0, pi = 0; (sb = SWAP_PCTRIE_LOOKUP_GE(
-	    &object->un_pager.swp.swp_blks, pi)) != NULL;
-	    pi = sb->p + SWAP_META_PAGES) {
+	res = 0;
+	for (sb = SWAP_PCTRIE_ITER_START(&iter,
+	    &object->un_pager.swp.swp_blks, 0); sb != NULL;
+	    sb = SWAP_PCTRIE_ITER_STEP(&iter, SWAP_META_PAGES)) {
 		for (i = 0; i < SWAP_META_PAGES; i++) {
 			if (sb->d[i] != SWAPBLK_NONE)
 				res++;
@@ -1827,17 +1828,17 @@
 static void
 swap_pager_swapoff_object(struct swdevt *sp, vm_object_t object)
 {
+	struct pctrie_iter iter;
 	struct swblk *sb;
 	vm_page_t m;
-	vm_pindex_t pi;
 	daddr_t blk;
 	int i, nv, rahead, rv;
 
 	KASSERT((object->flags & OBJ_SWAP) != 0,
 	    ("%s: Object not swappable", __func__));
 
-	for (pi = 0; (sb = SWAP_PCTRIE_LOOKUP_GE(
-	    &object->un_pager.swp.swp_blks, pi)) != NULL; ) {
+	for (sb = SWAP_PCTRIE_ITER_START(&iter,
+	    &object->un_pager.swp.swp_blks, 0); sb != NULL;) {
 		if ((object->flags & OBJ_DEAD) != 0) {
 			/*
 			 * Make sure that pending writes finish before
@@ -1915,7 +1916,7 @@
 			break;
 		}
 		if (i == SWAP_META_PAGES)
-			pi = sb->p + SWAP_META_PAGES;
+			sb = SWAP_PCTRIE_ITER_STEP(&iter, SWAP_META_PAGES);
 	}
 }
 
@@ -2144,6 +2145,8 @@
 swp_pager_meta_transfer(vm_object_t srcobject, vm_object_t dstobject,
     vm_pindex_t pindex, vm_pindex_t count, vm_size_t *moved)
 {
+	struct pctrie_iter iter;
+	struct pctrie *ptree;
 	struct page_range range;
 	struct swblk *sb;
 	vm_page_t m;
@@ -2156,17 +2159,17 @@
 
 	mc = 0;
 	m = NULL;
-	if (count == 0 || pctrie_is_empty(&srcobject->un_pager.swp.swp_blks))
+	ptree = &srcobject->un_pager.swp.swp_blks;
+	if (count == 0 || pctrie_is_empty(ptree))
 		goto out;
 
 	swp_pager_init_freerange(&range);
 	offset = pindex;
 	last = pindex + count;
-	for (;;) {
-		sb = SWAP_PCTRIE_LOOKUP_GE(&srcobject->un_pager.swp.swp_blks,
-		    rounddown(pindex, SWAP_META_PAGES));
-		if (sb == NULL || sb->p >= last)
-			break;
+	sb = SWAP_PCTRIE_ITER_START(&iter, ptree,
+	    rounddown(pindex, SWAP_META_PAGES));
+	for (; sb != NULL && sb->p < last;
+	    sb = SWAP_PCTRIE_ITER_STEP(&iter, SWAP_META_PAGES)) {
 		start = pindex > sb->p ? pindex - sb->p : 0;
 		limit = last - sb->p < SWAP_META_PAGES ? last - sb->p :
 		    SWAP_META_PAGES;
@@ -2191,8 +2194,7 @@
 		pindex = sb->p + SWAP_META_PAGES;
 		if (swp_pager_swblk_empty(sb, 0, start) &&
 		    swp_pager_swblk_empty(sb, limit, SWAP_META_PAGES)) {
-			SWAP_PCTRIE_REMOVE(&srcobject->un_pager.swp.swp_blks,
-			    sb->p);
+			SWAP_PCTRIE_ITER_REMOVE(&iter);
 			uma_zfree(swblk_zone, sb);
 		}
 	}
@@ -2292,6 +2294,7 @@
 vm_pindex_t
 swap_pager_find_least(vm_object_t object, vm_pindex_t pindex)
 {
+	struct pctrie_iter iter;
 	struct swblk *sb;
 	int i;
 
@@ -2300,7 +2303,7 @@
 
 	if (pctrie_is_empty(&object->un_pager.swp.swp_blks))
 		return (object->size);
-	sb = SWAP_PCTRIE_LOOKUP_GE(&object->un_pager.swp.swp_blks,
+	sb = SWAP_PCTRIE_ITER_START(&iter, &object->un_pager.swp.swp_blks,
 	    rounddown(pindex, SWAP_META_PAGES));
 	if (sb == NULL)
 		return (object->size);
@@ -2309,8 +2312,7 @@
 			if (sb->d[i] != SWAPBLK_NONE)
 				return (sb->p + i);
 		}
-		sb = SWAP_PCTRIE_LOOKUP_GE(&object->un_pager.swp.swp_blks,
-		    roundup(pindex, SWAP_META_PAGES));
+		sb = SWAP_PCTRIE_ITER_STEP(&iter, SWAP_META_PAGES);
 		if (sb == NULL)
 			return (object->size);
 	}