Project 3 Page Replacement in Linux

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Project 3Page Replacement in Linux

• CS-502, Operating SystemsFall 2007
• Due, Monday, November 12, 2007

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Review VM Page Replacement

• If there is an unused frame, use it.
• If there are no unused frames available, select a
  victim (according to policy) and
• If it contains a dirty page (M 1)
• write it to disk
• Invalidate its PTE and TLB entry
• Load in new page from disk (or create new page)
• Update the PTE and TLB entry!
• Restart the faulting instruction
• What is cost of replacing a page?
• How does the OS select the page to be evicted?

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Review The Best Page to Replace

• The best page to replace is the one that will
  never be accessed again
• Optimal Algorithm Beladys Rule
• Lowest fault rate for any reference string
• Basically, replace the page that will not be used
  for the longest time in the future.
• Beladys Rule is a yardstick
• We want to find close approximations

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Page Replacement Strategies and Algorithms

• NRU Not recently used
• FIFO First-in, First-out
• Second chance
• Page must migrate to top of queue twice
• Clock Second chance in a circular list
• Two-handed clock
• LRU Least Recently Used
• Unimplementable, but many approximations

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Page Replacement Algorithms (continued)

• Working Set
• WS Clock
• Combines Working Set and Clock
• (not discussed) Page buffering algorithms
• Silbershatz, 9.4.7

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Project 3

• Discover what your version of Linux kernel does
  about page replacement
• Identify
• Code modules and data structures
• Daemons
• Algorithms
• Watch it in action
• E.g., printk(), /proc entries, etc.
• Write a report
• 3-5 pages, explain and document

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Project 3 Resources

• Silbershatz, 9.4.7, 21.6.2.3
• Love, Chapter 15
• With recognition of Chapter 14
• Source code of Linux kernel 2.6.18.8-0.5
• Anything else you can find
• Each other
• And any friends you can con into helping!

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Project 3 Report

• How does page replacement really work
• Beyond what Love and Silbershatz say in the books
• What daemons run, who starts them, how often do
  they run, what triggers them, etc.
• pdflush. Any others?
• Identify code modules, functions, and data
  structures in kernel
• Describe any experiments you did to watch page
  replacement in action
• E.g., when running a big program such as kernel
  build

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Collaboration

• You may collaborate with each other in
• Research on-line
• Experimenting with kernel
• Studying kernel code
• Etc.
• You must write your own report in your own words
• 3-5 pages plus any data output from experiments

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Project Submission

• Due date Monday, November 12
• I.e., two weeks from today
• Submit report and data output via web-based
  Turnin system
• http//turnin.cs.wpi.edu8088/servlets/turnin.ss
• This is Project 3

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Questions?