Lazy Release Persistency

Fast non-volatile memory (NVM) has sparked interest in log-free data structures (LFDs) that enable crash recovery without the overhead of logging. However, recovery hinges on primitives that provide guarantees on what remains in NVM upon a crash. While ordering and atomicity are two well-understood primitives, we focus on ordering and its efficacy in enabling recovery of LFDs. We identify that one-sided persist barriers of acquire-release persistency (ARP)--the state-of-the-art ordering primitive and its microarchitectural implementation--are not strong enough to enable recovery of an LFD. Therefore, correct recovery necessitates the inclusion of the more expensive full barriers. In this paper, we propose strengthening the one-sided barrier semantics of ARP. The resulting persistency model, release persistency (RP), guarantees that NVM will hold a consistent-cut of the execution upon a crash, thereby satisfying the criterion for correct recovery of an LFD. We then propose lazy release persistency (LRP), a microarchitectural mechanism for efficiently enforcing RP's one-sided barriers. Our evaluation on 5 commonly used LFDs suggests that LRP provides a 14%-44% performance improvement over the state-of-the-art full barrier.