Energy Aware Persistence: Reducing the Energy Overheads of Persistent Memory

Next generation byte addressable nonvolatile memory (NVM) technologies like PCM are attractive for end-user devices as they offer memory scalability as well as fast persistent storage. In such environments, NVM's limitations of slow writes and high write energy are magnified for applications that need atomic, consistent, isolated and durable (ACID) updates. This is because, for satisfying correctness (ACI), application state must be frequently flushed from all intermediate buffers, including processor cache, and to support durability (D) guarantees, that state must be logged. This increases NVM access and more importantly results in additional CPU instructions. This paper proposes Energy Aware Persistence (EAP). To develop EAP, we first show that the energy related overheads for maintaining durability are significant. We then propose energy-efficient durability principles that mitigate those costs, an example being flexible logging that switch between performance and energy-efficient modes and a memory management technique that trades capacity for energy. Finally, we propose relaxed durability (ACI-RD) mechanism used under critical low energy conditions that do not affect correctness. The initial results for several realistic applications and benchmark show up to 2x reduction in CPU and NVM energy usage relative to a traditional ACID-based persistence.