How can mysql clog swap if there is free memory?

Question

MySQL

Good afternoon. Mysql is slowly filling swap day after day. Increasing memory doesn't help. Decided to use atop to track the situation.
Here are screenshots of the state with a difference of 30 seconds:
First:

Second:

I.e. there is free memory, but the displacement to swap still occurs. How can this even be?

Answer 1

https://habr.com/company/flant/blog/348324/ describes how and why in some detail.

Answer 2

unfreed but unused chunks of memory??