A Low-Overhead Encoding Scheme to Extend the Lifetime of Nonvolatile Memories

Emerging nonvolatile memories (NVMs) are promising to replace DRAM as main memory. However, NVMs suffer from limited write endurance and high write energy. Encoding method reduces the bit flips of NVMs by exploiting additional tag bits to encode the data. The effect of the encoding method is limited by the capacity overhead of the tag bits. In this article, we propose to exploit the space saved by compression to store the tag bits of the encoding method. We observe that the saved space size of each compressed cache line varies, and different encoding methods have different tradeoffs between capacity overhead and effect. To fully exploit the space saved by compression for improving lifetime, we select the proper encoding method according to the saved space size. To improve the compression coverage and compression ratio, we select an efficient compression scheme from two compression algorithms and provide more space for data encoding. Still, some data patterns cannot be compressed by any compression technique. We use the Flip-N-Write with 3.1% capacity overhead to encode uncompressible cache lines. The experimental results show that our scheme reduces the bit flips by 32.5%, decreases the energy consumption by 22.6% and improves the lifetime by 69.9% with 3.5% capacity overhead.