https://www.linuxbabe.com/ubuntu/4-tips-speed-up-ubuntu-16-04

2. Adjust Swappiness

We all know that RAM is way faster than hard drive.

Let’s do a little experiment: Boot your Ubuntu 16.04 system, open a few applications like Firefox, LibreOffice, Mozilla Thunderbird, Evince document viewer and then don’t do anything with it. Don’t suspend or hibernate it. Then after a few hours return to your Ubuntu 16.04. You will find that these applications are responding poorly to your mouse clicks because they were idle and swapped out to hard drive.

You can find in system monitor that Ubuntu is using swap space although you have plenty of free physical RAM.

This is due to the default swappiness value of Ubuntu. Swappiness is a Linux kernel parameter that controls how often Linux swap out idle processes to the swap space on your hard drive.

The value of swappiness is between 0 ~ 100. Lower value means Linux will use swap space less whereas higher value causes Linux to use swap space more often. The default value on Ubuntu is 60 which means when your computer uses up 40% of physical RAM, Linux kernel begins swapping.

You can use the following command to check the current value.

cat /proc/sys/vm/swappiness

It’s recommended to set a low value for swappiness so that Linux kernel will use as much physical RAM as possible. For example, to set swappiness to 10:

sudo sysctl vm.swappiness=10

Do not add space before and after the equal sign. This command tells Linux kernel to use swap space when 90% or more of physical RAM is used up.  This setting isn’t persistent.

To make it persistent across reboots, you need to edit a file.

sudo nano /etc/sysctl.d/99-sysctl.conf

At the end of this file, append the following line.

vm.swappiness=10

Save and close this file. (Press Ctrl+O to save, press Ctrl+X to exit) This tip is also applicable to your Ubuntu 16.04 server.