Every couple days something on my RHEL 7 box goes into a swapstorm and uses up all the memory. I think it’s Firefox, but I never figured out why, generally I have four different Firefoxes running with four different profiles, so it’s hard to tell which one’s failing (if it even is that). Anyway, sometimes it makes the screen lock crash or something, and I can’t get in, and I can never remember what process you have to kill to get back in, so here it is: gnome-shell. You have to killall -9 gnome-shell, and it lets you back in. Also killall -STOP firefox and killall -STOP "Web Content" are handy if the swapstorm is still under way.