100% disk usage lead to unusable system

If you install ubuntu Linux on a small disk space, like 6 GB. You can crash and make the system completable unusable simply by installing some games with Synaptic (Or downloading anything that take up disk space) . You get a notification of "100% disk is in use" and the system hangs and becomes slow. I have also experienced that it is impossible to log on to the computer because some file can't be written (Because there is no place to write the file?) . This bug can easily be removed by warning users when 80-90% of the disk space will become in use by downloading or installing programs. Now you can install as much as you want just by highlighting programs in Synaptic, and use up all your disk space in one click if you want. Without any warring or anything. This need to change.