UFS File-Based Optimization (FBO) Standard and Its Controversial Linux Kernel Patch

JEDEC, the standard body for the micro‑electronics industry, recently published version 1.0 of the Universal Flash Storage (UFS) File‑Based Optimization (FBO) extension. The specification defines an extended UFS electrical interface and storage device behavior that physically defragments the logical block address (LBA) ranges associated with particular files, aiming to mitigate performance degradation over time.

According to a Phoronix report on 2 November, a Xiaomi engineer submitted a set of Linux kernel patches that implement UFS FBO, claiming “better performance.” The engineer’s mail outlined the intended functionality as follows:

Host‑to‑device dialogue required for the feature: ◆ The host informs the device of the LBA range it is interested in, which is usually tied to a specific file and can be derived from the file’s iNode and offsets. ◆ The host queries the device for the current physical fragmentation level of that file. ◆ If needed, the host can instruct the device to perform defragmentation. ◆ After a successful defragmentation phase, the host may ask for the file’s new fragmentation level.

The patch series was promptly rejected by seasoned Linux kernel maintainer Christoph Hellwig, who harshly criticized the proposal. He quoted the engineer’s description and responded:

“This is a completely crazy idea. A file is a logical concept; it is not unique (it can have multiple references, snapshots) and can change at any time (defragmentation, garbage collection, deduplication). Whoever came up with this plan must be on crack, and it has nothing to do with the Linux kernel.”

At present, the likelihood of the UFS FBO patches being accepted into the Linux kernel appears extremely low.

Related links:

Phoronix article on UFS FBO

JEDEC JESD231 specification