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Virtual Memory

Virtual Memory. Instructor: Rob Nash Readings: Chapter 9. What IS the Free List?. A Mystery! Solved by our Text! See chapter 11 for more details “The free-space list, despite its name, might not be implemented as a list, as we discuss next” Jeopardy Style: “What is a linked list?”

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Virtual Memory

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  1. Virtual Memory • Instructor: Rob Nash • Readings: Chapter 9

  2. What IS the Free List? • A Mystery! Solved by our Text! See chapter 11 for more details • “The free-space list, despite its name, might not be implemented as a list, as we discuss next” • Jeopardy Style: “What is a linked list?” • “What is a bit vector?”

  3. Happy Holidays! (AdamB) • All of my TAs (save one) are completely booked with finals • The rewrite needs another pass that won’t be done today • If you aren’t done, focus on prep for the final • If you *are* done, turn in for extra reapers on the final • Reapers will be used to “buy off” problems.

  4. Administrivia • Today: More problems from Chapter 9 today • Exam Review • Evaluations • Lab help • Final Exam With Cookies: Next Tuesday

  5. VM Space (9.4) • 2^32 bytes of VM space • 2^18 physical memory size • Paging with a page size of 4096 bytes • (1) How many frames in this system? • (2) How many pages? • (3) Which bits are used as an index the page table, and which bits are the offset? • (4) VA:0x11123456 //How to determine PA? P (20) O(12)

  6. UNIX FS Features • The system uses any blocks • Multi-level page schemes

  7. Windows NTFS/XP • Uses consecutive blocks (clusters) • Uses a single-level page table • Working set minimum and maximums are assigned • FAT incorporates free-block accounting into the allocation data scheme • Where is our allocators in ThreadOS?

  8. Demand Paging(9.14) • Paging Disc with average access of 20 millis • Addresses use a page table lookup in MM • MM access time is 1 microsecond • What is the memory access time without a TLB? • What if we add a fast associative memory that can (virtually) eliminate the page table lookup • What is our AMAT if our TLB hit rate is 80%? • 95%?

  9. Thrashing(9.15) • Discussion 3

  10. The Working Set Parameter (9.17) • Consider the Working-set model • What is the effect of setting this sliding window too small? • What is the effect of setting this sliding window too large?

  11. LFU versus LRU (9.7) • How could LFU > LRU wrt page faults?

  12. Take-Home AMAT (9.5) • Assume demand paged memory, with the PT held in fast registers. • Page Fault : 8 millis • If page to replace is dirty, wb is 20 millis • Pages are dirty 70% of the time • What is the maximum acceptable pf rate if we want an effective access time of <=200 nanos?

  13. Take-Home • 9.13 • 9.17 • 9.7 • 9.8

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