Comment 114 for bug 1672297

FWIW, I have a pretty consistent reproduction of this on my 20.04 machine here. Restarting gnome-shell with Alt-F2 then "r" causes all the window management stuff to go away, but doesn't actually kill the process that's reporting the giant resident set size. Manually killing that pid also causes the WM chrome to disappear for a second and then pop back once a new gnome-shell process spawns. That one comes up almost instantly with a huge (but smaller, at least) RSS:

0] jbm@complexity:~/Downloads $ ps l 650626
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
0 1000 650626 2554 20 0 6884676 2449912 - Rsl ? 62:14 /usr/bin/gnome-shell
0] jbm@complexity:~/Downloads $ kill 650626

(run top to get the new PID)

130] jbm@complexity:~/Downloads $ ps l 665168
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
0 1000 665168 2554 20 0 6248912 1988284 poll_s Ssl ? 0:57 /usr/bin/gnome-shell

So, it's gone from 2449912 to 1988284. That isn't nothing: 2.3GiB vs 1.9GiB, but it's still a heck of a lot of RAM for a newly-spawned process.

Hope this report helps!