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Discussion Week 6

Discussion Week 6. TA: Kyle Dewey. Overview. Project #2 questions Project #2 test cases Exam sample questions Project #3 high level overview. Project #2 Error Conditions. Do not worry about error codes Still should check for error conditions for your own testing. Project #2 Questions?.

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Discussion Week 6

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  1. Discussion Week 6 • TA: Kyle Dewey

  2. Overview • Project #2 questions • Project #2 test cases • Exam sample questions • Project #3 high level overview

  3. Project #2 Error Conditions • Do not worry about error codes • Still should check for error conditions for your own testing

  4. Project #2 Questions?

  5. Project #2 Test Cases • In code/test • These will be used to test your code, along with similar variants of them • Altogether, they have wide coverage

  6. Some Cases • fork.c • ncat.c • test1.c

  7. Exam Sample Questions

  8. Question: “Do OSes actually swap anything anymore?”

  9. Relevance • Modern systems have tons of memory • Usually a lot more free memory than in use • Setups vary widely

  10. Memory Usage • Linux has the free command • Shows free and used memory, along with swap

  11. Occasional Webserver total used free shared buffers cachedMem: 3962 3782 179 0 181 3009-/+ buffers/cache: 591 3370Swap: 1983 0 1983

  12. Occasional Fileserver total used free shared buffers cachedMem: 496 481 14 0 270 65-/+ buffers/cache: 144 351Swap: 792 1 790

  13. CSIL Under Load total used free shared buffers cachedMem: 8072 7493 579 0 277 3292-/+ buffers/cache: 3923 4149Swap: 12229 205 12023

  14. Server After Load Spike total used free shared buffers cachedMem: 8002 7697 304 0 2098 4652-/+ buffers/cache: 946 7055Swap: 1811 353 1458

  15. Virtualization • Multiple OSes feed off the same memory • Memory tends to be the greatest limitation • Special software used to force OS to page in one VM when another is starved for memory

  16. Virtualized Memory 4 GB total 4 GB total Needs 3 GB Needs 2 GB OS1 OS2 Machine 4 GB total

  17. On Paging • Paging is a last resort mechanism • A private, lightly loaded system will likely never need it • In enterprise environments, it ranges from very nice to absolutely vital

  18. Project #3 Overview

  19. Part I • Need to implement paging • Tests will be so large as to need paging • Paging algorithm cannot be naive • Least recently used (LRU) • Second chance FIFO queue

  20. FIFO Queue Oldest Page Newest Page Page 1 Page 2 Page 3 Page 4 Page swapped in Page 2 Page 3 Page 4 Page 5 Oldest Page Newest Page

  21. FIFO + Second Chance Page 1 Ref: true Page 2 Ref: true Page 3 Ref: false Page 4 Ref: true Page swapped in Page 4 Ref: true Page 1 Ref: false Page 2 Ref: false Page 5 Ref: true

  22. Part 2 • Make the NACHOS filesystem more useful • Will be using the NACHOS disk for this • Flat file hierarchy

  23. Part 2 • Implement Create(), Open(), Remove(), List(), Seek(), Read(), ReadAt(), Write(), WriteAt(), and Length()

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