[$] Some buffer-heads cleanup work

Jan Kara has been working on cleaning up how buffer heads are used by some kernel filesystems. In a short filesystem-track session at the 2026 Linux Storage, Filesystem, Memory Management, and BPF Summit, he gave an update on that work and where it is headed. Topics included generic infrastructure to track buffer heads for metadata, a buffer-head cleanup for the Amiga filesystem, and some planned locking fixes.