Task: Memory Mapping

Navigate to the labs/lab-04/tasks/copy/ directory, and open the support/src directory. Here you will find these files:

• read_write_copy.c in which you will implement copying with read / write syscalls
• mmap_copy.c in which you will implement copying using mmap
• benchmark_cp.sh script which runs the two executables mmap_copy and read_write_copy

1. Complete the implementations for the read_write_copy.c and mmap_copy.c files. The goal is to copy the in.dat file to out.dat using the read / write syscalls and mmap respectively. Check your work by running the checker.sh script in the support/tests/ directory.

2. Once you have a working implementation, run the benchmark_cp.sh script to compare the performance of the two approaches. The output should look like this:

   student@os:~/.../drills/tasks/copy/support$ ./benchmark_cp.sh
   Benchmarking mmap_copy on in.dat
   time passed 54015 microseconds
   
   Benchmarking read_write_copy on in.dat
   time passed 42011 microseconds
   

   Run the script a few more times. As you can see, there isn’t much of a difference between the two approaches. Although we would have expected the use of multiple system calls to cause overhead, it’s too little compared to the memory copying overhead.

3. Add a sleep() call to the mmap_copy.c file after the files were mapped. Rebuild the program and run it. On a different console, use pmap to view the two new memory regions that were added to the process, by mapping the in.dat and out.dat files.

If you’re having difficulties solving this exercise, go through this reading material.