+/*
+ * Discussion: concurrent deletion of contiguous allocated ranges.
+ *
+ * Ensuring that merge of contiguous free ranges is always performed, we
+ * need to ensure locking of concurrent removal of contiguous allocated
+ * ranges one with respect to another. This is done by locking the
+ * ranges prior to and after the range to remove, even if that range is
+ * allocated. This serializes removal of contiguous ranges. The only
+ * cases for which there is no range to lock is when removing an
+ * allocated range starting at 0, and/or ending at the end of the key
+ * space.
+ */
+