Paging: Difference between revisions

The processor always fires a page fault exception when the present bit is cleared in the PDE or PTE regardless of the address. This means the contents of the PTE or PDE can be used to indicate a location of the page saved on mass storage and to quickly load it. When a page gets swapped to disk, use these entries to identify the location in the paging file where they can be quickly loaded from then set the present bit to 0. Similarly, blocks from disk can be mapped to memory this way. When a process accesses the memory-mapped region, a page fault occurs. The fault handler reads the appropriate tables, loads the disk block(s) into a page, and maps it. The process can then read/write to memory as if it were accessing the device directly. The contents of the page would then be written back to disk to save the changes.