Project 1: Memory Management





Overview
This assignment is related to virutal memory management inside OS. Although typically an OS can support more than one process, you only need to handle one process in this assignment. You will practice the management of page table and physical memory allocation by emulating what happens inside the OS kernel. Since we can't operate on real hardware and at the OS level, this project will design a simulator.

The homework will include three parts with a total of 80 points.
In this assignment, we are considering a tiny computing system with 1K bytes physical memory, and the virtual address has 12 bits (4096 bytes). Suppose that the size of virtual page/frame is 128 bytes (i.e., with 7 bits in the address as offset). Before starting your implementation, thinking about the following questions.

You may only go ahead when you fully understand the answer these questions. Talk to your classmate or ask help from TA or the instructor in case you have any confusions.
(1) What is the number of virtual pages for each process? ( Answer: 32 pages )
(2) How many physical pages (or frames) in total? ( Answer: 8 pages )
(3) How many entries in the page table for each process? ( Anwer: 32 entries )
If you can understand all of these questions, now you can proceed to design a paging system that implements one-level page table. We only use one-level page table for simplicity.

Part 1: 20 points
This is just to get you started. Assume that the page table of the process is like the following picture.

pagetable

Note that only several entries of the process' page table are listed as we will only use the first 7 entries in Part 1.

Create a directory called assign1 for this assignment. Write a main program called assign1part1.c for this part. The program will take only one parameter, the name of sequence file , which contains a sequence of logical memory accesses. Here, each logical addresses is saved as 8 bytes (unisgned long). Your program should read and analyze each logical address, and translate it into the corresponding physical addresses based on the given page table as shown in the above picture. Note: to simplify the work in Part 1, you can put the fixed mapping from page to frame as shown in the figure into an array before performing any address translation.

The logical memory address is saved in a binary format. To verify that you can read in the correct sequence of memory accesses, you can first print out the address that you have analyzed. You can test your program with the given simple test sequence file (part1testsequence), where the first address should be 0x0000000000000044 and the second one should be 0x0000000000000224.

You can also refer to the sample code to analyze the given sequence file. For each logical address in the sequence file, you will use the above given simple page table to perform the address translation and generate a corresponding physical address. You will output the translated physical address into a new file called output-part1test file. This output-part1test file should have the similar format as the given part1testsequence file as above (i.e., each physical address should use 8 bytes (as an unsigned long value) in the output file). In this assignment, we save each logical/physical address as 64 bits (8 bytes) to make the program to be more general.

Once you test your program with the above simple test sequene, which contains only 8 memory accesses, and you are sure the program performs correct address translation, you should use the following sequence file (part1sequence) as the input file for the logical address sequence to generate the translated physical addresses and put them in another file called output-part1. Then you can utilize the md5sum to compute their corresponding checksum, and you only need to write corresponding checksum into "status.txt" file.

Part 2: 40 points;

In this part, you will be designing the page table and handling the physical memory management. You will create two new source files in this part: phypages.c and pagetable.c, and a new main program named as assign1part2.c, plus any necessary header files. Here, phypages.c is used to manage the physical pages and pagetable.c will manage the page table for the process.

For this part, we also assume the same as above: the first physical frame/page is reserved for the OS, while other pages are freed initially. You will use a simple physical page allocation initially:
you will allocate the physical page in the order of frame number, starting from 1, 2, 3, ....... If there are some physical pages that are available, you will always allocate from the free list at first.

Once there is no free physical frame, you need to use one of the page replacement policies to choose a physical frame to free. We will use the LRU policy at first, which means the page that is least recently used (accessed) will be freed at first.

Note that, once a frame is selected to be freed, you need to do two things:
(1) First, you should change the old entry of page table so that we don't have two virtual pages pointing to the same physical frame.
(2) Second, you need to change the entry of target page in the page table to point to the frame. At the same time, you may also set up the reverse mapping on the physical page so that we can find the page table entry when we will assign this frame to other entries.

If a page is just accessed recently, you should update the corresponding the placement of its physic frame so that this frame will not be evicted soon (based on the LRU policy).

The input address sequence of the program is the same as in part 1. Thus, you should be able to utilize the same analyzing function to get the corresponding virtual address, and then transfer it to a physical address for each memory access in the file.

In the end, you can use the same function of part 1 to output to the translated physical address sequences into a file. For the following input sequence file part2sequence, the program should generate the output file as output-part2.

Similar to part 1, you will only need to report the md5sum checksum for the output file output-part2. In addition, your program should count the number of page faults for the given logical address sequence in the file and the result should be reported in "status.txt.

Part 3: 20 points. Making your design to be adaptive to any situation

For this part, we do not assume the size of a page, size of virtual memory, size of physical memory. You will design a system that can be adaptive to any situation of these different parameters. To get the bonus points, you should list whether you have implemented part 3 in your "status.txt" file. Also, you should briefly explain how to implement this part in comparison to the first two parts.

You should have a new main program named as assign1part3.c, and your program should accept the following parameters:

./assign1 BytesOfPage SizeOfVirtualMemory SizeOfPhysicalMemory SequenceFile

where the first parameter BytesOfPage specifies the number of bytes in each physical frame and virtual page. The second parameter SizeOfVirtualMemory is the size of virtual memory in bytes. The third one SizeOfPhysicalMemory is the size of physical memory in bytes. The fourth one SequenceFile is the name of the file that contains the sequence of memory access logical addresses that need to be translated.

To test your program's Part 3 functions, you can use the parameters specified in "Part 2", and your program should generate the same output file as output-part2. In the end, give an argument why you think the implementation is correct.

Submission guideline

You will submit through the blackboard. Please including the "status.txt", and a "source" directory that includes all source code and Makefile.
"source" directory: mandatory
This directory should include all of your source code (*.c, *.h) and Makefile. Without the soure code, you can only get 50% points of your earned at most.
status.txt: manadatory
You should include a status report in the file status.txt. Here, the status report in status.txt should include whether you have complete Parts 1 and 2 successfully. If successful, include the md5sum checksums for each part on the test input sequences. For Part 2: you should also include the number of page faults for test sequence. Part 3: please include the required description for the bonus points. Please also give brief description of what is working and what progress was made on the part that is not working. There will be a severe penalty (50% off) if the "status.txt" is not aligned with your source code. If there is no "status.txt", you won't get any points.

Please compress all of these files into a zipped file and name it as "abc123.zip". abc123 should be replaced with your abcid.