1. Today’s agenda ~10min: file system (UNIX) ~1hr: final review + Q&A
CS354-Fall2018

2. FINAL: Wednesday December 12th, 3:30 PM, Fowler Hall
Bring your ID (will be checked)
Closed everything (book, notes, calculator, cell phone, laptop, other electronic, discussion)
Comprehensive: Chapters 1-10, 12-14, and supplementary materials + labs + xinu’s source codes
After Midterm: a heavier weight
Comprehensive questions cover materials before and after Midterm
The exam will cover chapters 1-10, 12-14, and 19 of our XINU textbook, as well as all slides and additional notes covered in class. For Prof Comer's slides, the exam will cover CS354Presentation1.pdf to CS354Presentation6.pdf posted on Piazza. The introduction slides (1courseoverview), scheduling supplement, synchronization supplement, and virtual memory supplement are also included.
CS354-Fall2018

3. FINAL Questions T/F will use bubblesheet
Multi-choice will use bubblesheet
Other questions
Similar to those in Midterm
CS354-Fall2018

4. A Big Picture Please read Midterm review as well
OS overview (ch1, ch3)
Process management (Core to OS)
Process: concurrent execution (ch2, ch6)
Process scheduling ( ch 5 + supplement)
Process synchronization (ch 7 + supplement)
Inter-processing communication (Message passing) (ch8)
Memory management
Low-level memory management (ch9)
High-level memory management and virtual memory (ch10 + supplement)
Device management
Interrupt (ch12)
Device driver (ch14)
Clock management (ch13)
File system (ch19)
CS354-Fall2018

5. Quiz (Piazza) Check quiz solutions for both sections
All quizzes for section 2
+ Quiz5 in section 1: file systems
Question on quizs?
CS354-Fall2018

6. Process states System calls State-transition HOW? When to call?
What else needed?
WHY
Data structures, global variables used
CS354-Fall2018

7. Materials before Midterm (skipped today)
Please read Midterm review as well
Process management (Core to OS)
Process: concurrent execution (ch2, ch6)
Process scheduling ( ch 5 + supplement)
Process synchronization (ch 7 + supplement)
CS354-Fall2018

8. Message passing Why do we need message passing? How?
receive(), recvclr()
send()
CS354-Fall2018

9. Sample Questions What is difference between receive() and recvclr()?
Synchronous vs asynchronous
Will the process state change after calling recvclr()? (or receive())? If no, please explain. If yes, what are new states?
recvclr(): no change
receive(): RECEIVING (resched() called) if no message
CS354-Fall2018

10. Low-level Memory Management
Why?
Heap and stack
How?
Physical memory: bulk
Free memory block list
Allocation Strategies
First-fit
Last-fit
Best-fit
getmem(), freemem(), getstk(), freestk()
CS354-Fall2018

11. Sample Questions Explain the results given certain operations Block 0
getmem(128), feemem(128)
getstk(256), freestk(256) 32
512
1024
128 64 32
128
CS354-Fall2018

12. High-level memory management
Why?
Abstract memory resources
How?
Bufferpool: for each subsystem
Creation: init
Allocation: dynamic
Virtual memory
Process: loading into memory
Swapping, segmentation, paging
On-demand paging
CS354-Fall2018

13. High-level memory management
Demanding paging
Page table (mapping from PHY memory to virtual memory)
Page fault
Page replacement
Strategies: FIFO, LRU (and its variants), Belady (optimal), Global clock algorithms
Multitasking
Work set algorithm
CS354-Fall2018

14. Sample Questions
Given the following page reference string: Show the results for each paging replacement algorithms
Count the number of page faults
Compare which is better and explain why it is not good
CS354-Fall2018

15. Device Management Interrupt Why? (OS, Devices) How?
OS, Processor (hardware), device hardware
interrupt mask, disable/restore
Dispatcher
Interrupt handler
CS354-Fall2018

16. Device Management Three rules: Which process calls interrupt handler?
Any current process
Will interrupts be allowed during its execution?
disable interrupt when running dispatcher
Disable interrupt when the interrupt handler loads global variables…. (process stack ….)
Will interrupt handlers change the process state?
Yes, but only from current to ready (eligible state)
Others are not allowed (wait, suspend, sleep, receive, not allowed)
CS354-Fall2018

17. Device drivers Upper-half and lower-half Device table
Lower-half: ~ interrupt handler
Device table
Abstract operations: open, read, write, seek, control …
Row and column
CS354-Fall2018

18. Clock management Interrupt Clock handler
sleepms(), sleep()
Delta list: sleeping processes
Why? (O(1) operations)
Intertd(), unsleep(), wakeup()
CS354-Fall2018

19. Sample Questions Is context switch be allowed in an interrupt handler?
List potential interactions between processes and interrupt handling?
Interrupt pile up…
Update sleepq given different sleep or unsleep or wakeup operations? 3 A 2 B 2 C 3 D
CS354-Fall2018

20. File System Why? How? (many design choices)
File: a better abstract than I/O (bytes)
OS – DISK (hardware)
How? (many design choices)
Typed vs. untyped
caching, sharing, allocation …
XINU: directory, index blocks, data blocks
Unix: differences (much more powerful)
i-node (metadata, data points: direct and indirect)
Blocks are loaded dynamically when needed
CS354-Fall2018

21. Sample Questions Why XINU doesn’t scale?
What are pros and cons of a UNIX FS?
Given a file size, calculate how many blocks (sectors) are needed?
Describe how the following file access works
Open()
Read() or write()
Seek()
CS354-Fall2018

22. Some recap questions When to call resched()?
Describe how the OS runs when one process (A) requires input from disk (file systems: loading a block) while other processes (B and C) are running which also open and read a large file (10KB).
Interaction between OS and Device I/O
Process, memory management, device driver, file system
A: File system  disk I/O; Interrupt from disk I/O  new process -> resched()  back to A (some time later…)
What if page faults? (page replacement)
CS354-Fall2018

23. Final word: Go through all the materials
Slides, textbooks, quizzes, labs, XINU codes
Understanding HOW and WHY
==================
Extra office hours
Monday (Dec 10): 1:30PM-3:45PM
Tue (Dec 11): 10AM-11:AM, 1:00PM-2PM
Ask questions on Piazza
Grades posted at BB before 8AM, Dec 17 (Monday)
Contact me before 5PM, Dec 17 if you have any questions
Remind: course evaluation (a few minutes only!)
Good luck!
CS354-Fall2018