Swapping the Page Tables to Disk

Finally, we discuss the relaxation of one final assumption.

Thus far, we have assumed that page tables reside in kernel-owned physical memory. Even with our many tricks to reduce the size of page tables, it is still possible, however, that they may be too big to fit into memory all at once. Thus, some systems place such page tables in kernel virtual memory, thereby allowing the system to swap some of these page tables to disk when memory pressure gets a little tight. We’ll talk more about this in a future chapter (namely, the case study on VAX/VMS), once we understand how to move pages in and out of memory in more detail.