diff --git a/src/crush/CrushWrapper.cc b/src/crush/CrushWrapper.cc
index e5af5405f72..22b0524158a 100644
--- a/src/crush/CrushWrapper.cc
+++ b/src/crush/CrushWrapper.cc
@@ -7,7 +7,7 @@
 #define dout_subsys ceph_subsys_crush
 
 
-void CrushWrapper::find_roots(set<int>& roots) const
+void CrushWrapper::find_takes(set<int>& roots) const
 {
   for (unsigned i=0; i<crush->max_rules; i++) {
     crush_rule *r = crush->rules[i];
@@ -20,6 +20,17 @@ void CrushWrapper::find_roots(set<int>& roots) const
   }
 }
 
+void CrushWrapper::find_roots(set<int>& roots) const
+{
+  for (int i = 0; i < crush->max_buckets; i++) {
+    if (!crush->buckets[i])
+      continue;
+    crush_bucket *b = crush->buckets[i];
+    if (!_search_item_exists(b->id))
+      roots.insert(b->id);
+  }
+}
+
 bool CrushWrapper::subtree_contains(int root, int item) const
 {
   if (root == item)
@@ -86,7 +97,7 @@ int CrushWrapper::remove_item(CephContext *cct, int item)
   return ret;
 }
 
-bool CrushWrapper::_search_item_exists(int item)
+bool CrushWrapper::_search_item_exists(int item) const
 {
   for (int i = 0; i < crush->max_buckets; i++) {
     if (!crush->buckets[i])
diff --git a/src/crush/CrushWrapper.h b/src/crush/CrushWrapper.h
index 048eb3dee5c..1cbdf1192a7 100644
--- a/src/crush/CrushWrapper.h
+++ b/src/crush/CrushWrapper.h
@@ -230,6 +230,18 @@ public:
   }
 
 
+  /**
+   * find tree nodes referenced by rules by a 'take' command
+   *
+   * Note that these may not be parentless roots.
+   */
+  void find_takes(set<int>& roots) const;
+
+  /**
+   * find tree roots
+   *
+   * These are parentless nodes in the map.
+   */
   void find_roots(set<int>& roots) const;
 
   /**
@@ -248,7 +260,7 @@ private:
    * @param i item
    * @return true if present
    */
-  bool _search_item_exists(int i);
+  bool _search_item_exists(int i) const;
 public:
 
   /**