Question

Operating System question:

Say we have a process running in a paged memory system, and we want to track which pages it accesses in the specific order it does so. How could we do this?

I was thinking we could write the page to the string every time it needs to be loaded into the TLB, but then my OS wouldn’t be able to track the ordering of references (and number of references) to each page in the TLB, unless somehow every every memory access I could check the TLB. Overall I’m finding the problem to be a bit confusing…

Assume each page table entry is 64 bits, 20 bits for the virtual page, and 20 bits for the corresponding physical frame. A couple of bits are status/privilege, but there are a few “free” bits to work with.

Thanks.

EDIT – an example: if the operating system has page sizes of 1000, and the process accesses some addresses like 1234, 5660, 1220, 7442, … then the page reference string would look like 1,5,1,7,…

Answer 1

One option is to mark all pages of the process as inaccessible and whenever there’s a page fault, mark the faulting page(s) as accessible, record the page number(s) in your “string” and then let the process execute one instruction and repeat everything from the beginning (mark all as inaccessible, etc).

You may not always be able to do the above if your the code that’s doing all of this is not running in the kernel. This depends a lot on the hardware and OS. You may get close to it on Windows, though, see this question and my answer to it.