Supporting filesystems in persistent memory

Posted Sep 3, 2014 10:11 UTC (Wed) by smurf (subscriber, #17840)
In reply to: Supporting filesystems in persistent memory by lpremoli
Parent article: Supporting filesystems in persistent memory

Looking at PRAMFS's tech page on SourceForge, I seriously doubt its suitability for multi-terabyte file systems. A free-block bitmap, linear directories, and no hard links? No way.

Supporting filesystems in persistent memory

Posted Sep 3, 2014 21:48 UTC (Wed) by ssl (guest, #98177) [Link] (1 responses)

> free block bitmap

By the way, is there a comparision how modern FS keep tabs on free space?

Supporting filesystems in persistent memory

Posted Sep 12, 2014 19:40 UTC (Fri) by vedantk (guest, #88435) [Link]

Btrfs: Btrfs keeps track of the space it allocates in its extent tree [1]. Holes between extents correspond to free space. There's a free space cache but no explicit free space tracking [2].

ZFS: ZFS appends allocation/deallocation metadata to a log, which it replays into an in-memory AVL tree. You can read about ZFS-style space maps in [3].

Those are the only two `modern' (read: non-bitmappy) approaches I know of, but I could be missing others.

[1]: https://btrfs.wiki.kernel.org/index.php/Btrfs_design#Exte...

[2]: https://btrfs.wiki.kernel.org/index.php/Glossary

[3]: https://blogs.oracle.com/bonwick/en/entry/space_maps