I/O Passthru: Upstreaming a flexible and efficient I/O Path in Linux

New storage interfaces continue to emerge fast on Non-Volatile Memory Express (NVMe) storage. Fitting these innovations in the general-purpose I/O stack of operating systems has been challenging and time-consuming. The NVMe standard is no longer limited to block-I/O, but the Linux I/O advances historically centered around the block-I/O path. The lack of scalable OS interfaces risks the adoption of the new storage innovations. We introduce I/O Passthru, a new I/O Path that has made its way into the mainline Linux Kernel. The key ingredients of this new path are NVMe char interface and io_uring command. In this paper, we present our experience building and upstreaming I/O Passthru and report on how this helps to consume new NVMe innovations without changes to the Linux kernel. We provide experimental results to (i) compare its efficiency against existing io_uring block path and (ii) demonstrate its flexibility by integrating data placement into Cachelib. FIO peak performance workloads show 16-40% higher IOPS than block path.