It is in fact system protection from memory overflow. If you are this type of person who doesn't want swap, consider using this application.

When the amount of memory used exceeds certain value a notification is shown. It includes a button to kill a process with the highest memory usage.

$USER/.config/memp/memp.conf

maxMemAllowed=80 # minimum memory usage in percents to trigger the notification

• libnotify

Ubuntu:

sudo apt-get install libnotify-dev

Arch:

sudo pacman -S libnotify