What's zero page? Where can I read more about it? Wikipedia[1] suggests in modern operation systems "actually make the zero page inaccessible to trap uses of NULL pointers".
Ya its not that Zero page. This is just a page of zeros. When you allocate virtual memory the OS gives you the virtual allocation but the physical allocation points to the page of zeros. So when you read you get zeros. Only when you write does the OS allocate a real physical page of memory (which is should zero before handing over to the application). The reason why is important for the random read test is that if he does not initialize memory he might not be reading from dram but constantly reading the zero page which would be very fast.