Bcachefs Merges New On-Disk Format Version For Linux 6.11, Working Toward Defrag

Ahead of the Linux 6.11-rc4 kernel release coming up later today, some more Bcachefs file-system patches were merged this weekend for this experimental copy-on-write file-system.

This latest round of Bcachefs fixes includes a new on-disk format version. This latest rev is for adding another disk accounting counter to be used for counting disk usage and the number of extents per inode number. This "bcachefs_metadata_version_disk_accounting_inum" is needed for Bcachefs to track fragmentation.

In the future this new disk accounting counter will be used for helping Bcachefs implement defragmentation support. This will also count disk usage per inode in all snapshots that later can be used to expose that data to users.

What comes to mind when thinking of file-system defragmentation...

In addition to working toward defragmentation support, this latest Bcachefs fixes pull also takes care of a possible performance problem:

"One performance issue we've observed is threads spinning when they should be waiting for dirty keys in the key cache to be flushed by journal reclaim, so we now have hysteresis for the waiting thread, as well as improving the tracepoint and a new time_stat, for tracking time blocked waiting on key cache flushing."

More details on this latest batch of Bcachefs fixes from Kent Overstreet via this Git merge. Look for these fixes and more in the Linux 6.11-rc4 kernel test release due out this evening.