Update from July 10, 2018—KB4338819 (OS Build 17134.165) has done something to the drivers on my GTX960 4G , so I had to reinstall them.
Before I did that csrss.exe was taking up 2.2G of VRAM, and about 25-30% of its processor. That was really annoying, because it was as if I was playing The Witcher 3 (fans working to keep the temperature below 60 degrees), and also there were micro-freezes
in other apps.
P.S. A day after the problem has returned. Thank you microsoft.