RAMinate: Hypervisor-based Virtualization for Hybrid Main Memory Systems

In the future, STT-MRAM will achieve larger capacity and comparable read/write performance, but incur orders of magnitude greater write energy than DRAM. To achieve large capacity as well as energy-efficiency, it is necessary to use both DRAM and STT-MRAM for the main memory of a computer. In this paper, we propose a hypervisor-based hybrid memory mechanism (RAMinate) that reduces write traffic to STT-MRAM by optimizing page locations between DRAM and STT-MRAM. In contrast to past studies, our mechanism works at the hypervisor level, not at the hardware or operating system level. It does not require any special program at the operating system level nor any design changes of the current memory controller at the hardware level. We developed a prototype of the proposed system by extending Qemu/KVM and conducted experiments with application benchmarks. We confirmed that our page replacement mechanism successfully worked for unmodified operating systems and dynamically diverted memory write traffic to DRAM. Our experiments also confirmed that our system successfully reduced write traffic to STT-MRAM by approximately 70% for tested workloads, which results in a 50% reduction in energy consumption in comparison to a DRAM-only system.