Sequoia: A High-Endurance NVM-Based Cache Architecture

Emerging nonvolatile memory technologies, such as spin-transfer torque RAM or resistive RAM, can increase the capacity of the last-level cache (LLC) in a latency and power-efficient manner. These technologies endure 10(9)-10(12) writes per cell, making a nonvolatile cache (NV-cache) with a lifetime of dozens of years under ideal working conditions. However, nonuniformity in writes to different cache lines considerably reduces the NV-cache lifetime to a few months. Writes to cache lines can be made uniformly by wear-leveling. A suitable wear-leveling for NV-cache should not incur high storage and performance overheads. We propose a novel, simple, and effective wear-leveling technique with negligible performance overhead of <0.4% for memory-intensive workloads. Our proposal consists of two mechanisms: 1) a wear-leveling mechanism within each cache set that slightly increases main memory write-back traffic and LLC miss rate and 2) a novel technique to reduce cache interset variation which causes minimum interference with normal cache operation. Using these mechanisms, we show that the lifetime of the NV-cache is boosted up to 13x for different cache configurations.