+ * radix_tree_shrink - shrink height of a radix tree to minimal
+ * @root radix tree root
+ */
+static inline void radix_tree_shrink(struct radix_tree_root *root)
+{
+ /* try to shrink tree height */
+ while (root->height > 0) {
+ struct radix_tree_node *to_free = root->rnode;
+ void *newptr;
+
+ BUG_ON(!radix_tree_is_indirect_ptr(to_free));
+ to_free = radix_tree_indirect_to_ptr(to_free);
+
+ /*
+ * The candidate node has more than one child, or its child
+ * is not at the leftmost slot, we cannot shrink.
+ */
+ if (to_free->count != 1)
+ break;
+ if (!to_free->slots[0])
+ break;
+
+ /*
+ * We don't need rcu_assign_pointer(), since we are simply
+ * moving the node from one part of the tree to another. If
+ * it was safe to dereference the old pointer to it
+ * (to_free->slots[0]), it will be safe to dereference the new
+ * one (root->rnode).
+ */
+ newptr = to_free->slots[0];
+ if (root->height > 1)
+ newptr = radix_tree_ptr_to_indirect(newptr);
+ root->rnode = newptr;
+ root->height--;
+ /* must only free zeroed nodes into the slab */
+ tag_clear(to_free, 0, 0);
+ tag_clear(to_free, 1, 0);
+ to_free->slots[0] = NULL;
+ to_free->count = 0;
+ radix_tree_node_free(to_free);
+ }
+}
+
+/**