OpenMem: Hardware/Software Cooperative Management for Mobile Memory System

Hybrid memory systems, comprised of emerging non-volatile memory (NVM) and DRAM, have been proposed to address the growing memory demand of current mobile applications. NVM technologies have higher capacity density, minimal static power consumption, but longer access latency and limited write endurance compared to DRAM. The different characteristics of these two memory classes, however, pose new challenges for memory system design. Ideally, pages shall be placed or migrated between the two types of memories according to the data objects’ access properties. Prior works use the OS for placement and migration in these systems, but at the cost of high software latency incurred by related kernel processes. Hardware approaches can avoid these latencies, however, hardware’s vision is constrained to a short time window of recently memory request, due to the limited on-chip resources.In this work, we propose OpenMem: a hardware-software cooperative approach to address placement and migration within hybrid memory systems, that combines the execution time advantages of pure hardware approaches with the data object properties in a global scope. We emulate OpenMem on an FPGA board with embedded ARM CPU, and run a set of benchmark applications from SPEC 2017 and PARSEC. Experimental results show that OpenMem reduces energy consumption by 44.6% with only a 16% performance degradation compared to an all-DRAM memory system. Further, writes to the NVM are reduced by 14% versus a hardware-only approach, extending the NVM device lifetime.