COMP 3430 – Operating Systems
Paging part 3
April 18th, 2022
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By the end of today’s lecture, you should be able to:
▶ Compare and contrast methods for address translation.
▶ Compare and contrast the solution of multi-level page tables with file system implementations.
The Woggle-Bug Book (Public Domain)
Term test 2
▶ Rank review topics
Paging and segmentation
Paging and segmentation are similar, but different.
Let’s look at some questions.
Drawers and boxes. (Pexels License)
Paging. (Pixabay License)
Paging and segmentation solve the same problem.
How do I make processes think they have an entire address space by mapping virtual addresses to physical addresses?
Paging avoids external fragmentation, but suffers from speed and size issues.
▶ Speed issues are addressed with a TLB (cache)
▶ Size issues can be addressed with different data structures
(directories).
▶ … at the cost of speed/performance.
Paging file systems?
Paging and file systems seem pretty different. ▶ Different levels of the memory hierarchy. ▶ Persistent storage vs ephemeral/volatile
Different like different kinds of fruit. (Pixabay License)
Paging file systems?
They are similar, though! Let’s look at some figures.
OSTEP Chapter 40 pg 4
OSTEP Chapter 20
Paging file systems?
▶ Virtual memory: base and bounds → segmentation → paging. ▶ Paging is a good, general purpose solution.
▶ Speed issues solved with caching.
▶ Size issues solved with data structures.
▶ File systems and paging: Similarities when you squint!
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