Supporting Dynamic Translation Granularity for Hybrid Memory Systems

Hybrid memory has become a promising new solution for meeting ever growing memory capacity demands in a cost-effective way. In hybrid memory systems, the fast and high bandwidth memory is used to store performance-critical data, while the slow and low bandwidth memory provides capacity backup. In supporting such hybridization, virtual memory is the key mechanism, which can combine different memory components to a single memory view. For efficient translation for virtual memory, page size has been growing. However, the hybrid memory support requires fine-grained migration to quickly move only necessary memory portions to the precious fast memory. To address the challenges posed by the conflicting goals in the hybrid memory support based on virtual memory, this paper investigates decoupling of address translation into a two-step process. With the two-level translation, the critical core-side TLBs perform the translation to an intermediate address space, and the memory-side translation provides the actual physical location in memory devices. As the second-level translation handling page migration across different memory types, is decoupled from the first-level translation, it allows dynamic adjustment of its mapping granularity to improve the efficiency of translation and data reuse in the fast memory. This paper proposes a hardware architecture which identifies the memory access behavior of an application online and selects the best mapping granularity for the second-level translation.