NRU: Page fault on writing?
The idea is to mark a read/write page as read-only when loading it into memory (or after writing it out). If it is written to, a fault will occur. When handling the fault, the operating system looks at it's tables, and notices it should be writeable. So it can record it as "written to" (modified) in it's tables, make it read/write, and allow the operation to proceed. Later writes just add insult to injury, no need to keep track of them.