you can use resource controls to limit/allocate a specific amount of memory to a specific user such as user 'oracle'. This can be done with the use of projects. When a user log in or starts a task..etc.., they would use the project setup for them.
The good thing is this can be done on the fly with out a reboot, but in order to make it permanent a different command set is used and a reboot is required.
Look up resource management to find more info on it.