defragmenting non-files only

defragmenting non-files only

[Eric Wong]

I'm wondering how much fragmentation affects users with large
active Maildirs where files are frequently created and removed.

I'm avoiding a blanket `btrfs fi defrag -r` to reduce storage
wear for files which won't live long.

So some questions:

1. how to monitor fragmentation of subvolume/extent tree or
   anything else which filefrag(8) doesn't seem to report
   fragmentation for?

2. does `btrfs fi defrag $DIR' work only for that directory?
   In other words, can I `btrfs fi defrag $TOPLEVEL_DIR` and
   expect subdirectories to be defragmented?

   Or should I do:

	find $TOPLEVEL_DIR -type d -print0 | xargs -0 btrfs fi defrag
   ?

Thanks.