When will "Uncollected Garbage" be deleted?

September is about garbage collection for me, 11 days of trying to solve my 13.5TB node. In the last few days, I’ve been trying to speed things up because the load has cut my expected money in half. Now I’m trying to reduce the shared space in the config.
The question is, how normal is it that the used-space-filewalker, retain and piece:trash processes run concurrently on that satellite?