Method, apparatus and product for data cloning in a memory-based file systems. A content of each object of the file system is retained in data units and represented using a tree of the nodes comprising tree nodes and leaf nodes. The file system utilizes a volatile resource usage collection and volatile reference counters for each node of the nodes. In response to mounting the file system, a storage retaining a file system metadata is scanned to compile the volatile resource usage collection and the volatile reference counters. In response to a determination to reuse a pointed node of a tree of an object by a pointing node, a volatile reference counter of the pointed node is updated and the pointing node is atomically set, using a single instruction, to point to the pointed node.