Re: Does btrfs filesystem defragment -r also include the trees?

[David Sterba <dsterba@suse.cz>]

On Thu, Apr 20, 2023 at 08:37:07AM -0400, Remi Gauvin wrote:
> I have recently experienced that btrfs defragment (by itself, without
> -r) of a subvolume can dramatically improve performance when accessing
> very large directories.  I would go so far as to call it critical
> maintenance when working with gtk3 based file managers.
> 
> What I am not clear on, however, does adding the -r *also* defragment
> the subvolume extent tree, or do the two commands needs to be run
> separately to get the full effect?

No, -r does not defragment the extent tree, so if you really want to
defragment the extent tree, then you need to run it separately and
without -r.

Originally there was only the extent tree defragmentation which was
confusing when defrag got a directory as an argument, then it always
defragmented the extent tree but did not descend recursively. Then the
-r was added and the bare directory path discouraged. It still works
though.

I've checked if this is documented, it seems to (btrfs-filesystem,
section defrag):

"NOTE: Directory  arguments  without -r do not defragment files
recursively but will defragment certain internal trees (extent tree and
the subvolume tree). This has been confusing and could be re- moved in
the future."

but if you think it's not clear enough please suggest in what way it
could be extended or what's missing.