CS 1550 – Project 3: VM Simulator
Due: Sunday, July 15, 2018, by 11:59pm
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.
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: ClockNumber of frames: 8Total memory accesses: 1000000Total page faults: 181856Total writes to disk: 29401
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/ 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 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);
Implementing OPT in a naïve fashion will lead to unacceptable performance. It should not take more than 5 minutes to run your program.
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.
One of the major contributions the university provides for the AFS filesystem is nightly backups. However, the /u/OSLab/ partition 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 to your ~/private/ directory frequently!
Loss of work not backed up is not grounds for an extension. You have been warned.
You need to submit:
Make a tar.gz file as in the first assignment, named USERNAME-project3.tar.gz
Copy it to ~jrmst106/submit/1550 by the deadline for credit.