Persistent memory provides data persistence at main memory level and enables memory-level storage systems. To ensure consistency of the storage systems, memory writes need to be transactional and are carefully moved across the boundary between the volatile CPU cache and the persistent memory. Unfortunately, the CPU cache is hardware-controlled, and it incurs high overhead for programs to track and move data blocks from being volatile to persistent. In this paper, we propose a software-based mechanism, Blurred Persistence, to blur the volatility-persistence boundary, so as to reduce the overhead in transaction support. Blurred Persistence consists of two techniques. First, Execution in Log executes a transaction in the log to eliminate duplicated data copies for execution. It allows the persistence of volatile uncommitted data, which can be detected by reorganizing the log structure. Second, Volatile Checkpoint with Bulk Persistence allows the committed data to aggressively stay volatile by leveraging the data durability in the log, as long as the commit order across threads is kept. By doing so, it reduces the frequency of forced persistence and improves cache efficiency. Evaluations show that our mechanism improves system performance by 56.3% to 143.7% for a variety of workloads.
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