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Unformatted text preview: y that it is thrashing.
Aside: Counting page faults. You can monitor the number of page faults (and lots of other information) with the Unix getrusage function. End Aside. 10.4 VM as a Tool for Memory Management
In the last section we saw how virtual memory provides a mechanism for using the DRAM to cache pages from a typically larger virtual address space. Interestingly, some early systems such as the DEC PDP-11/70 supported a virtual address space that was smaller than the physical memory. Yet virtual memory was still a 494 CHAPTER 10. VIRTUAL MEMORY useful mechanism because it greatly simpliﬁed memory management and provided a natural way to protect memory. To this point we have assumed a single page table that maps a single virtual address space to the physical address space. In fact, operating systems provide a separate page table, and thus a separate virtual address space, for each process. Figure 10.9 shows the basic idea. In the example, the page table for process maps VP 1 to PP 2 an...
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