[$] Some buffer-heads cleanup work

Jan Kara has been workingon cleaning up how bufferheads are used by some kernel filesystems. In a shortfilesystem-track session at the 2026 Linux Storage,Filesystem, Memory Management, and BPF Summit, he gave an update onthat work and where it is headed. Topics included generic infrastructureto track buffer heads for metadata, a buffer-head cleanup for the Amigafilesystem, and some planned locking fixes.