Comment 46 for bug 1672297

There is a memory leak generating window previews on gnome shell and since pressing the Super key generates windows previews the memory usage grows exponentially. For me Gnome Shell eats about 100-150 MB every day I leave it running.

I tested this both on an Intel graphics machine and on a VM, in both Artful and Bionic. Both times clean install.

1. on a clean boot open System Monitor and Terminal side by side (or System Monitor and any other window)
2. press Super wait for the window preview and then press ESC (repeat this several times)
3. Observe the memory usage for Gnome Shell System Monitor grow

You can also reproduce this by installing the Alternate Tab extension (https://extensions.gnome.org/extension/15/alternatetab/) which also generates window previews.

1. Alt+Tab between Terminal and System Monitor and watch the Gnome Shell memory usage grow every time.

Another user on reddit also came to a similar conclusion: https://www.reddit.com/r/gnome/comments/7teono/possible_fix_to_improve_gnome_lag/

Effectively gnome shell becomes unusable even on 8 GB of RAM after a week of usage.
I solve the issue by running ALT+F2 and 'r' every morning. People who are not technical of course will not do this and have a horrible experience.