Prof. Dr. Frank Bellosa
Lukas Werling

Abstract
Persistent Memory (PMEM) is a new non-volatile byte-addressable storage technology. While slower than DRAM, it offers significantly higher bandwidth and lower latencies when compared to SSDs. These characteristics make it a good option for improving I/O and in particular synchronous write performance. There have already been many projects working in different layers of the I/O stack aiming to achieve that goal. Most of them, however, fail to utilize the full hardware potential, require non-trivial changes to the kernel or replace existing file systems,
thus resulting in increased complexity and feature duplication.
In this thesis, we present DPWC, a Device Mapper module for the Linux kernel which uses PMEM as a write cache for a regular SSD device. In contrast to many other works in the field, DPWC easily integrates with unmodified existing file systems. We use a fast on-PMEM caching structure inspired by ZIL-PMEM [40] and optimize it specifically for Intel Optane hardware. DPWC achieves significant speed-ups (1.5-2.05x) in most multi-threaded write workloads compared to the standard write cache implementation (dm-writecache) included
in the Linux kernel. Unfortunately, these gains are made at the expense of performance in mixed read and write scenarios, but further optimizations for these cases may be possible.

BibTex:

@bachelorthesis{bozhinov22PNEM Write Cache,
  author = {Ilia Bozhinov},
  title = {Reducing Synchronous Write Latency With a PMEM Write Cache in the Device Mapper Layer},
  type = {Bachelor Thesis},
  year = 2022,
  month = april # "13",
  school = {Operating Systems Group, Karlsruhe Institute of Technology (KIT), Germany}
  }