Comment by nvme0n1p1

Your distro may vary on the policies around this, but the way the stack generally works, is that whatever shared libraries, and their memory resources, which haven't been touched in a while, are put into swap. So if you've run a few programs, left them open or whatever, switched the UI to other things and whatever over a period of a day, or even a few hours/minutes (its a knob), then bits of those programs will have gone cold. The local libraries and static things that haven't been executed - in a while - will move into that qualification.

You can tweak this, it is indeed a local-system configuration thing that a Linux user should know and think about - and maybe - if your distro has such a thing as a policy about it - this ought to be considered as well.

For example, I use Ubuntu Studio, precisely because it is generally well set up, swap-wise, to absolutely not interfere with audio performance (note: this DAW has been rock solid for decades) .. but every distro has its own 'medium ground' to consider when setting this.

The thesis/antithesis for/against swap is un-useful. Swap is a knob, not a switch.

Maybe not what's happening in your case, but stuff that is in swap will not be moved back to memory unless there's a need for it, so if you did have memory pressure at time 1, which resolved at time 2, then you might still see a lot of swap in use at time 3.