bcachefs

Posted Feb 24, 2025 18:52 UTC (Mon) by tim-day-387 (subscriber, #171751)
In reply to: bcachefs by koverstreet
Parent article: Filesystem support for block sizes larger than the page size

Lustre would benefit from a filesystem agnostic transaction API (at least, in kernel space). The OSD layer is essentially implementing that. We're making a push to get Lustre included upstream and the fate of OSD/ldiskfs/ext4 is one of the big open questions. Having a shared transaction API would make that much easier to answer.

bcachefs

Posted Feb 24, 2025 21:37 UTC (Mon) by Cyberax (✭ supporter ✭, #52523) [Link] (1 responses)

How does Lustre currently handle transactions? Especially rollbacks?

It looks like transactions in Lustre are more like an atomic group of operations, rather than something long-lived? I.e. you can't start a transaction, spend 2 hours doing something with it, and then commit it?

bcachefs

Posted Feb 25, 2025 16:49 UTC (Tue) by tim-day-387 (subscriber, #171751) [Link]

Currently, Lustre hooks into ext4 transactions in osd_trans_start() and osd_trans_stop() [1]. So the transactions aren't long-lived and are usually scoped to a single function. Lustre patches ext4 (to create ldiskfs) and interfaces with it directly. But it'd probably be better to have a generic way for filesystems to (optionally) expose these primitives. Infiniband has a concept of kverbs - drivers can optionally expose an interface to in-kernel users. We'd could do something similar for transaction handling.

[1] https://git.whamcloud.com/?p=fs/lustre-release.git;a=blob;...