Z-Journal: Scalable Per-Core Journaling


Jongseok Kim and Cassiano Campes, Sungkyunkwan University; Joo-Young Hwang, Samsung Electronics Co., Ltd.; Jinkyu Jeong and Euiseong Seo, Sungkyunkwan University


File system journaling critically limits the scalability of a file system because all simultaneous write operations coming from multiple cores must be serialized to be written to the journal area. Although a few scalable journaling approaches have been proposed, they required the radical redesign of file systems, or tackled only a part of the scalability bottlenecks. Per-core journaling, in which a core has its own journal stack, can clearly provide scalability. However, it requires a journal coherence mechanism because two or more cores can write to a shared file system block, so write order on the shared block must be preserved across multiple journals. In this paper, we propose a novel scalable per-core journal design. The proposed design allows a core to commit independently to other cores. The journal transactions involved in shared blocks are linked together through order-preserving transaction chaining to form a transaction order graph. The ordering constraints later will be imposed during the checkpoint process. Because the proposed design is self-contained in the journal layer and does not rely on the file system, its implementation, Z-journal, can easily replace JBD2, the generic journal layer. Our evaluation with FxMark, SysBench and Filebench running on the ext4 file system in an 80-core server showed that it outperformed the current JBD2 by up to approx. 4000 %.

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@inproceedings {273794,
author = {Jongseok Kim and Cassiano Campes and Joo-Young Hwang and Jinkyu Jeong and Euiseong Seo},
title = {{Z-Journal}: Scalable {Per-Core} Journaling},
booktitle = {2021 USENIX Annual Technical Conference (USENIX ATC 21)},
year = {2021},
isbn = {978-1-939133-23-6},
pages = {893--906},
url = {https://www.usenix.org/conference/atc21/presentation/kim-jongseok},
publisher = {USENIX Association},
month = jul,

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