1. An apparatus, comprising: a converter configured to dynamically convert a structure of a data representation stored in a memory, wherein the structure is selectively converted between a sparse format and a non-sparse format, and wherein the data representation identifies data allocations in a persistent storage device; wherein the converter is configured to convert the structure of the data representation based at least in part on a memory size of the sparse format as compared to a memory size of the non-sparse format during run-time.