Due to the Linux 4.21 merge window expected to open up next week just prior to Christmas, some kernel subsystem maintainers who won't be around in the days ahead have been sending in their pull requests early. Among those with early feature pulls is David Sterba continuing to oversee the Btrfs file-system development.

Most notable to Btrfs in Linux 4.21 is the long-awaited support for swap files on Btrfs is now working but with a number of limitations for the time being, such as no compression or snapshotting.

Other Btrfs work for Linux 4.21 includes the ability to assign a new file-system UUID without overwriting all metadata blocks, more balance messages being printed to the system log, and a variety of file-system fixes.

The complete list of the dozens of patches for Btrfs can be found via this pull request.