How much percentage should zram take?

I'm setting up zram on my server, let's say I have 4GB ram, should zram take 3.5G or 1G or something in between? What trade off will I have when going to the extremes? And, for example I have a single thread that's taking 30mb of ram in zram, when this thread gets invoked by other threads, does the system uncompress all the zram in ram and run the thread in ram, or the system just read and write the zram in place?