This has been an ongoing issue with X11 compositers like marco, unity and cinnamon etc... Ifind especially with an Nvidia GPU that as the system runs longer after a number of weeks or a number of months the GUI just gets slower and slower. It's not something you'll instantly notice but just a hint of lag here or there that gets worse. One hint you'll find is by watching nvidia-smi and checking the utilization you will start seeing random spikes of 80-100% even without maxi........