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By The Linux Camp News, October 21, 2026
The development-tree update removes an unnecessary size restriction for software atomic writes on reflink-enabled XFS, while preserving hardware alignment limits.
XFS updates merged into the Linux 7.4 development tree on October 21, 2026 UTC, including a correction to software atomic-write size limits. This is development integration, not a stable release. The broader batch concentrates on fixes and cleanup, particularly scrub and online repair, rather than major new features. 2 1 4
Previously, when storage advertised atomic-write support, XFS capped its software maximum at the largest power-of-two factor of the allocation-group size. That calculation accommodated aligned hardware requests, but also constrained a software path that did not need that alignment. The affected software limit applies with reflink enabled; its copy-on-write, or COW, path writes data out of place instead. 4
The fix calculates the software limit from group size and moves the alignment restriction to xfs_get_atomic_write_max_opt(), which reports the hardware-offload limit. A write that cannot become one naturally aligned hardware atomic request can use the COW path instead. This separates two capabilities; it does not increase the device's native atomic-write size. 4 3
For applications using atomic writes, the practical difference can be a larger advertised maximum. In the patch author's example, stx_atomic_write_unit_max rose from 32 KiB to 64 MiB, while stx_atomic_write_unit_max_opt remained 16 KiB. These are reported capability values, not throughput or latency measurements. 4
When evaluating this change, compare the software maximum and hardware-optimal maximum separately rather than treating a larger software value as faster hardware. Do not assume the example's 64 MiB applies to every filesystem: group size participates in the calculation. The sources retrieved October 21, 2026 do not establish affected released-kernel ranges or stable backports, so they cannot determine a deployed system's patch status. 4 1