CrossFS: A Cross-layered Direct-Access File System


Yujie Ren, Rutgers University; Changwoo Min, Virginia Tech; Sudarsun Kannan, Rutgers University


We design CrossFS, a cross-layered direct-access file system disaggregated across user-level, firmware, and kernel layers for scaling I/O performance and improving concurrency. CrossFS is designed to exploit host- and device-level compute capabilities. For concurrency with or without data sharing across threads and processes, CrossFS introduces a file descriptor-based concurrency control that maps each file descriptor to one hardware-level I/O queue. This design allows CrossFS’s firmware component to process disjoint access across file descriptors concurrently. CrossFS delegates concurrency control to powerful host-CPUs, which convert the file descriptor synchronization problem into an I/O queue request ordering problem. To guarantee crash consistency in the cross-layered design, CrossFS exploits byte-addressable nonvolatile memory for I/O queue persistence and designs a lightweight firmware-level journaling mechanism. Finally, CrossFS designs a firmware-level I/O scheduler for efficient dispatch of file descriptor requests. Evaluation of emulated CrossFS on storage-class memory shows up to 4.87X concurrent access gains for benchmarks and 2.32X gains for real-world applications over the state-of-the-art kernel, user-level, and firmware file systems.

Open Access Media

USENIX is committed to Open Access to the research presented at our events. Papers and proceedings are freely available to everyone once the event begins. Any video, audio, and/or slides that are posted after the event are also free and open to everyone. Support USENIX and our commitment to Open Access.

@inproceedings {258868,
author = {Yujie Ren and Changwoo Min and Sudarsun Kannan},
title = {CrossFS: A Cross-layered Direct-Access File System},
booktitle = {14th {USENIX} Symposium on Operating Systems Design and Implementation ({OSDI} 20)},
year = {2020},
isbn = {978-1-939133-19-9},
pages = {137--154},
url = {},
publisher = {{USENIX} Association},
month = nov,
Artifact Evaluated

Presentation Video