DV-NVLLC: Efficiently guaranteeing crash consistency in persistent memory via dynamic versioning

Byte-addressable persistent memory provides fast access to persistent data, but problems such as system crashes and power failures may cause persistent data corruption. Though using traditional logging or copy-on-write(COW) can guarantee crash consistency, it results in extra storage and performance overheads, and also shortens the lifetime of persistent memory. To reduce the overhead caused by logging and COW, existing mechanisms ensure consistency by leveraging the different versions of data in a non-volatile CPU cache(NV cache) and persistent memory. However, the performance loss is still significant compared with the system that does not enforce crash consistency. To improve the performance, we analyze the overheads of memory transactions quantitatively, including the access pattern of cache and the asymmetry of read and write of persistent memory media. Based on our analysis, we propose DV-NVLLC which uses the NV cache as the last-level cache(NV-LLC). In NVLLC the dynamic versioning method is used to manage different versions of data based on their update frequency. Hot data is updated-of-place in NV-LLC. Cold data is updated by version control between NV-LLC and persistent memory. Therefore, DV-NVLLC can reduce write traffic to persistent memory while guaranteeing crash consistency. Our evaluation shows that DV-NVLLC improves performance by 18% to 57%, and reduces write traffic to persistent memory by 35% to 89% compared with the state-of-the-art design that uses NV cache as the last-level cache.