FIRM: Fair and High-Performance Memory Control for Persistent Memory Systems
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Byte-addressable nonvolatile memories promise a new technology, persistent memory, which incorporates desirable attributes from both traditional main memory (byte-addressability and fast interface) and traditional storage (data persistence). To support data persistence, a persistent memory system requires sophisticated data duplication and ordering control for write requests. As a result, applications that manipulate persistent memory (persistent applications) have very different memory access characteristics than traditional (non-persistent) applications, as shown in this paper. Persistent applications introduce heavy write traffic to contiguous memory regions at a memory channel, which cannot concurrently service read and write requests, leading to memory bandwidth underutilization due to low bank-level parallelism, frequent write queue drains, and frequent bus turnarounds between reads and writes. These characteristics undermine the high-performance and fairness offered by conventional memory scheduling schemes designed for non-persistent applications. Our goal in this paper is to design a fair and high-performance memory control scheme for a persistent memory based system that runs both persistent and non-persistent applications. Our proposal, FIRM, consists of three key ideas. First, FIRM categorizes request sources as non-intensive, streaming, random and persistent, and forms batches of requests for each source. Second, FIRM strides persistent memory updates across multiple banks, thereby improving bank-level parallelism and hence memory bandwidth utilization of persistent memory accesses. Third, FIRM schedules read and write request batches from different sources in a manner that minimizes bus turnarounds and write queue drains. Our detailed evaluations show that, compared to five previous memory scheduler designs, FIRM provides significantly higher system performance and fairness.