Best way to monitor snapshot disk space?

Does your PHP manage to clean up the ROS list of snapshots that is kept apart from the BtRFS structures? I ask because I have a share for which I had done some manual subvolume deletes (really to try and get rid of a massive number of unwanted snapshots, rather than clicking on them one at a time in the web UI). BtRFS happily obliged, but ROS still thinks there are hundreds of them, and won't let me blash this share into oblivion -- it "fails" to delete the snapshots. :( Not precisely the problem you were looking to solve here, I know. But if you worked out how to update that list in your PHP, that could be useful for me in this case. :D