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Question 6 (v1) [10 points]
In a paged virtual memory system, two processes are active. The system has 10 physical page frames numbered from 0 to 9. Each physical frame has 1024 bytes. The page tables of the two processes are shown below, where each row specifies: the physical frame number, the referenced (R), the modified (M), and the valid (V) bits. An entry with V = 1 is a valid entry.
Process 1 Page Table Process 2 Page Table Frame R M V Frame R M V 06011 00001
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14111 17101 25101 28001 30000 32011 41101 40000 59101 53111
The system uses a global Clock Algorithm. Replacement decisions are made periodically, rather than on demand. At the end of each period, the Clock Algorithm scans half of the frames. If a frame is selected for replacement during the scan then it is placed on a free list and its associated valid bit is reset to zero. When a page fault occurs, the system chooses a page from the free list for replacement. When a modified frame is added to the free list, its page is not copied back to secondary storage until the page is actually replaced by a new page.
1. Assume that the above page tables exist at the end of a period, and that the clock hand points at frame zero. (This means that the algorithm will consider frames zero, one, two, three, and four.) Show the page tables of the two processes after the algorithm runs. Indicate which frames will be added to the free list.
2. Immediately after the replacement algorithm runs, process 2 runs and attempts to read logical address 3500. Does this reference result in a page fault? Explain.
Circle one: YES NO
3. If the answer to the above part is yes, show the contents of process 2¡¯s page table after the page fault handler has run and the virtual address has been translated successfully by the MMU. Assume that the free list contains those frames that were placed there when the replacement algorithm was run (in the above part of the question). Fill the following table to indicate which pages if any, Indicate which pages if any, will be copied from memory to disk, and which pages, if any will be copied from disk to memory.
(logical page, corresponding frame)
copied from memory to disk copied from disk to memory
University of Alberta examination University of Alberta examination
University of Alberta examination
University of Alberta examination University of Alberta examination
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