It's not just 3 seconds for a button click, every time I've run out of RAM on a Linux system, everything locks up and it thrashes. It feels like 100x slowdown. I've had better experiences when my CPU was underclocked to 20% speed. I enable swap and install earlyoom. Let processes die, as long as I can move the mouse and operate a terminal.
Yup, this is a thing. It happens because file-backed program text and read-only data eventually get evicted from RAM (to make room for process memory) so every access to code and/or data beyond the current 4K page can potentially involve a swap-in from disk. It would be nice if we had ways of setting up the system so that pages of code or data that are truly critical for real-time responsiveness (including parts of the UI) could not get evicted from RAM at all (except perhaps to make room for the OOM reaper itself to do its job) - but this is quite hard to do in practice.
