Project 3: Virtual Memory Simulator Solution

Project Overview




In class, we have been discussing various page replacement algorithms that an Operating System implementer may choose to use. In this project, you will compare the results of four different algorithms on traces of memory references. While simulating an algorithm, you will collect statistics about its performance such as the number of page faults that occur and the number of dirty frames that had to be written back to disk. When you are done with your program, you will write up your results and provide a graph that compares the performance of the various algorithms.




The four algorithms for this project are:




Opt – Simulate what the optimal page replacement algorithm would choose if it had perfect knowledge




Clock – Use the better implementation of the second-chance algorithm




FIFO – Implement first-in, first-out




NRU – Pick a not recently used page using the R and D bits.




You may write your program in C/C++, Java, Perl, or Python as long as it runs on thoth.cs.pitt.edu.




Implement a page table for a 32-bit address space. All pages will be 4KB in size. The number of frames will be a parameter to the execution of your program.




Project Details




You will write a program called vmsim that takes the following command line:




./vmsim –n <numframes -a <opt|clock|fifo|nru [-r <refresh] <tracefile




The program will then run through the memory references of the file and display the action taken for each address (hit, page fault – no eviction, page fault – evict clean, page fault – evict dirty).




When the trace is over, print out summary statistics in the following format:




Algorithm: Clock


Number of frames:
8
Total memory
accesses:
1000000
Total page faults:
181856
Total writes
to disk:
29401



Implementation




We are providing three sample memory traces. The traces are available at /u/OSLab/original/ in the files bzip.trace.gz, swim.trace.gz, and gcc.trace.gz













Each trace is gzip compressed, so you will have to copy each trace to your directory under /u/OSLab/username and then decompress it like:




gunzip bzip.trace.gz




In the resulting trace file is a sequence of lines, each having a memory address in hexadecimal followed by a R or W character to indicate if that access was a read or a write. For example, gcc.trace starts like this:




0041f7a0 R




13f5e2c0 R




If you are writing in C, you may parse each line with the following code:




unsigned int address;




char mode;




fscanf(file, "%x %c", &addr, &mode);




Note




Implementing OPT in a naïve fashion will lead to unacceptable performance. It should not take more than 5 minutes to run your program.




Write Up




For NRU, you have a refresh parameter to set. Try to find a good refresh period that works well. You do not need to find the absolute minimum, just approximately how long to wait. Plot your results in a graph and discuss why your choice of refresh seemed to be the best.




For each of your four algorithms (with NRU using the proper refresh you determined), describe in a document the resulting page fault statistics for 8, 16, 32, and 64 frames. Use this information to determine which algorithm you think might be most appropriate for use in an actual operating system. Use OPT as the baseline for your comparisons.




For FIFO, with the three traces and varying the total number of frames from 2 to 100, determine if there are any instances of Belady’s anomaly. Discuss in your writeup.




File Backups




One of the major contributions the university provides for the AFS filesystem is nightly backups. However, the /u/OSLab/ partition on thoth is not part of AFS space. Thus, any files you modify under your personal directory in /u/OSLab/ are not backed up. If there is a catastrophic disk failure, all of your work will be irrecoverably lost. As such, it is my recommendation that you:












Backup all the files you change under /u/OSLab or QEMU to your ~/private/ directory frequently!




Loss of work not backed up is not grounds for an extension.




Requirements and Submission




You need to submit:




Your well-commented program’s source



A document (.DOC or .PDF) detailing the results of your simulation as described above



DO NOT submit the trace files!



Make a tar.gz file named USERNAME-project3.tar.gz and upload it to CourseWeb by the deadline.




Grading Sheet/Rubric






Item




Grade












vmsim program main skeleton




10%




OPT implementation
15%




CLOCK implementation




15%




FIFO implementation
15%




NRU implementation




15%




Writeup (Determining the optimal value of the refresh parameter)
10%




Writeup (The graph plotting the number of page faults versus the




10%




number of frames and your conclusions on which algorithm would be










best to use in a real OS)










Writeup (FIFO Analysis)
10%

































































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