1. CS Honors Research: Memory Mapped files in Linux Kousha Najafi Prof: Eddie Kohler Grad Student: Steve VanDeBogart 10.25.07

2. Research Topic Explore Linux memory-mapped-file system call performance. Find and Resolve inconstancies when compared to read system call

3. Memory-mapped files Mmap maps a process’s memory to a file directly on disk. On page fault, the corresponding page of the file is loaded directly to userspace memory from file. Mmap is used to load up programs from disk to memory.

4. read system call Kernel requests information from disk Disk reads file and copies it to kernel memory Kernel copies requested data to userspace This theoretically should be slower than mmaped files because of the additional copy…

5. mmap vs read (Forwards) 128MB rampreadmmap min4.81s8.29s max5.34s19.46s avg4.97s13.68s stdev0.17s4.95s Reading 256MB file on system with 128MB memory

6. mmap vs read (Backwards) 128MB rampreadmmap min23.20s17.20s max23.47s25.84s avg23.33s23.02s stdev0.08s3.32s Reading 256MB file on system with 128MB memory

7. Checkpoints Figure out what causes the slowdown Figure out what causes the inconsistencies Come up with theory to fix problem Try to code a patch to fix problem