I installed the 590 pre relaese and it didn't help too...
I also must say that some days ago I replaced Avast with another security software (avira) but my problem didn't solved (maybe it is not related to avast)
It seems that when I use my Hard disks like copying files or dowsloading ,the memory usage goes up more rapidly (maybe the problem is related to hard) but I can't find a solution for my problem until now