Limiting RAM usage during performance tests

I have to run some performance tests, to see how my programs work when the system runs out of RAM and the system starts thrashing. Ideally, I would be able to change the amount of RAM used by the system.

I haved tried to by boot my system (running Ubuntu 10.10) in single user mode with a limited amount of physical memory, but with the parameters I used (max_addr=300M, max_addr=314572800 or mem=300M) the system did开发者_C百科 not use my swap partition.

Is there a way to limit the amount of RAM used by the total system, while still using swap space?

The point is to measure the total running time of each program as a function of the input size. I am not trying to pinpoint performance problems, I am trying to compare algorithms, which means I need accuracy.

Write a simple c program which

• Will allocate large amount of memory.
• Keep on accessing allocated memory random to try to keep in main memory (in an infinite loop).

Now run this program (one or few processes) so that you allocate enough memory to cause the thrashing of process you are testing.