Emerging nonvolatile memory technologies (NVRAM) promise the performance of DRAM with the persistence of disk. However, constraining NVRAM write order, necessary to ensure recovery correctness, limits NVRAM write concurrency and degrades throughput. We require new memory interfaces to minimally describe write constraints and allow high performance and high concurrency data structures. These goals strongly resemble memory consistency. Whereas mem-ory consistency concerns the order that memory operations are observed between numerous processors, persistent memory systems must constrain the order that writes occur with respect to failure. We introduce memory persistency, a new approach to designing persistent memory interfaces, building on memory consistency. Similar to memory consistency, memory persistency models may be relaxed to improve performance. We describe the design space of memory persistency and desirable features that such a memory system requires. Finally, we introduce several memory persistency models and evaluate their ability to expose NVRAM write concurrency using two implementations of a persistent queue. Our results show that relaxed persistency models accelerate system throughput 30-fold by reducing NVRAM write constraints.
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