https://bugs.freedesktop.org/show_bug.cgi?id=100239
--- Comment #25 from Michel Dänzer michel@daenzer.net --- (In reply to Bruno Jacquet (Xaapyks) from comment #23)
So I'd say the issue is still there.
Maybe you have a ~/.drirc or other drirc file which gets picked up and disables radeonsi_zerovram? (E.g. due to ever starting the old "driconf" application with a driver which supported the option)