NEAR: A Novel Energy Aware Replacement Policy for STT-MRAM LLCs

As the technology node shrinks, leakage power becomes a bottleneck for processor performance and memory capacity scalings. Spin Torque Transfer Magnetic Random Access Memory (STT-MRAM) has negligible leakage power, fast access speed, high integration density and non-volatility. Therefore, it is a promising candidate for the last level cache design. However, it suffers from high write energy and slow write speed. In the paper, we observe that the traditional cache replacement policy is not optimal when applied to STT-MRAM from the energy consumption perspective. So we propose a novel write energy aware cache replacement policy, which utilizes a MinHash function to identify the similarities between the cache line to be written back and candidates for the replacement. The cache line with the highest similarity is chosen as the victim. In addition, we propose a new metric for cache replacement considering both performance and write energy to improve the replacement policy further. The experimental results show that our proposed policy can reduce write energy by 33.6% on average compared to the state-of-the-art Least Recently Used (LRU) replacement policy with only 0.5% performance penalty and negligible hardware overhead.