BTRFS subvolume deletions and their space

[oshunluvr]

I did some clean up this morning and thought it might be interesting to see just how much reported space is taken by a snapshot.

Here's df after each deletion:

/dev/sdd3          482289664 334805436 144553236  70% /subvol 
/dev/sdd3          482289664 334805712 144552984  70% /subvol 
/dev/sdd3          482289664 334227328 145108624  70% /subvol 
/dev/sdd3          482289664 333908896 145411376  70% /subvol
/dev/sdd3          482289664 333756276 145556740  70% /subvol
/dev/sdd3          482289664 333206816 146086112  70% /subvol
/dev/sdd3          482289664 323968428 154682252  68% /subvol <---
/dev/sdd3          482289664 323969072 154681728  68% /subvol
/dev/sdd3          482289664 316123004 162434204  67% /subvol
/dev/sdd3          482289664 313093124 165316956  66% /subvol
/dev/sdd3          482289664 310871164 167420916  65% /subvol
/dev/sdd3          482289664 307099764 171115972  65% /subvol
/dev/sdd3          482289664 283063972 195036764  60% /subvol

I saw as I deleted, the older snapshots were larger so more space was freed as expected. Midpoint in the list I finished all the root snapshots and started in on /home snapshots.
The arrow notes a subvolume that had two other subvolumes within it, which explains the large jump in size at that point.
The last once was done long ago of my /home and I had removed a bunch of stuff from my /home after that snapshot so it was very large.

The real oddities are two new-ish snapshots that actually show a reduction in free space. I can only assume this has to do with how btrfs reports free space to the OS.

Anyway - not a scientific study, I just though it was interesting. Here's a calculated list of the reported changes in free space:

-252
555640
302752
145364
529372
8596140
-524
7752476
2882752
2103960
3695056
23920792

The odd-balls really stick out. Now, what do I do with 50GB of newly freed space?