LightWSP: Whole-System Persistence on the Cheap

Whole-system persistence (WSP) has recently attracted more interest thanks to its transparency and performance benefits over partial-system persistence where users are not only burdened by complex persistent programming but also incapable of using DRAM as LLC. Nevertheless, existing WSP work either introduces high hardware cost or causes non-trivial performance overhead. To this end, this paper presents LightWSP, a compiler/architecture co-design scheme that can achieve WSP in a lightweight yet performant manner. LightWSP compiler partitions program into a series of recoverable regions (epochs) with their live-out registers checkpointed, while LightWSP hardware persists the stores of the regions-whose boundary serves as a power failure recovery point-enforcing crash consistency; LightWSP leverages the battery-backed write pending queue (WPQ) of a memory controller as a redo buffer, i.e., all stores are first buffered in WPQ and then persisted together in non-volatile memory (NVM) at each region end. In this way, no matter when power failure happens, NVM is never corrupted by the stores of the power-interrupted region, facilitating correct recovery. In particular, LightWSP supports multiple memory controllers on the cheap without costly speculation/misspeculation handling mechanisms used by prior work. The experimental results with 38 applications show that LightWSP incurs only an average of 9.0% run-time overhead. This is on par with the state-of-the-art work, that complicates the core microarchitecture significantly with its intrusive design for memory controller speculation, yet the hardware cost of LightWSP is near zero (0.5B per core).