One more thing. Disabling the disk cache is a very bad idea because no matter how much internal memory you may have it will always get full, the reason for this being discribed above. That means that once the internal memory gets full and it always will, Linux will need to have place to put that memory page. If it doesn't have virtual disk memory where it can put it, it will be forced to kill processes who uses a lot of memory just to free space.
This creates major instabillity and danger.
How can you have a disk cache if you don't have a disk by the way????