How often is kernel "touching" swap partition?

Question

I am going to buy new laptop with two drives, one SSD and one HDD and I want to place swap partition on HDD which will be most time unused and therefore spinned down. Problem is, that I don't know, if or how often is kernel touching swap space even if there is lot of free memory and thus spinning HDD up.

Answer 1

You should partition your drives anyway: a small, like 1G, partition for /boot. For swap, the old Received Wisdom was 2-2.5 times RAM; these days, it's "make swap to be 2G (for emergencies). Put swap on the SSD, I *guess*... if it's enterprise grade, and not "consumer grade", which will eventually give up with too many writes.

Answer 2

There's a kernel tunable called "swappiness" [1] to control that. You can add an entry in /etc/sysctl.conf like this:

vm.swappiness=0

...and the kernel will avoid, as much as it can, to use swap.