1. ecs150 fall 2010 final Name: Student ID: Email: Score: ___/32
Open book and totally 5 questions (4% or 8% each), 12 pages.
Please write precise and clean answers. But, please try to give at least partial answers as I will give partial credits. Please READ the questions VERY CAREFULLY before putting down the final answer. And, also please mark your answer clearly. You can use the back of the pages. Every page of this exam book needs to be returned back.
If we suspect any cheating behavior, we will pass the case to the academic committee immediately.
Score: ___/32
12/06/2010
ecs150 fall 2010, final

2. Q-01
(Soft Updates, Snapshot and Background FSCK, 8%) If we remove Soft Update mechanism from our File system implementation and the file system crashes, then we CANNOT use this file system IMMEDIATELY right after rebooting and taking a SNAPSHOT for background FSCK. Please state/explain the reason and show a DETAILED counter example. It is very important that, in your example, you need to specify which meta data will NOT be “copied on write” and causing a UNSAFE condition (please describe what that condition is) for using the FS immediately.
12/06/2010
ecs150 fall 2010, final

3. Q-01
(continued …)
12/06/2010
ecs150 fall 2010, final

4. 1st memory disk Q-02 DE5 DE7 (empty) iN(DE5) (empty) DE7 (empty)
(Soft Update, 8%) In each of the following diagrams, we have TWO directory blocks and TWO I-Node blocks. The first row shows the initial values of memory and disk BEFORE the synchronization. And, the second row shows a step-by-step sequence of block updates following the rules of “Soft Update” to synchronize the memory/disk. HOWEVER, the first sequence (this and next slide, p.4 & p.5) is worse than the second sequence (the next two slides, p.6 & p.7) for one performance-related reason. Please state the reason as your answer.
1st
memory
disk
DE5
DE7
(empty)
iN(DE5)
(empty)
DE7
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
DE2
(empty)
iN(DE2)
(empty)
DE3
iN(DE3)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
iN(DE7)
DE8
(empty)
iN(DE8)
iN(DE7)
DE5
DE7
(empty)
iN(DE5)
(empty)
DE7
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
DE2
(empty)
iN(DE2)
(empty)
DE3
iN(DE3)
(empty)
(empty)
(empty)
iN(DE3)
(empty)
(empty)
(empty)
(empty)
iN(DE7)
DE8
(empty)
iN(DE8)
iN(DE7)
DE5
DE7
(empty)
iN(DE5)
(empty)
DE7
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
iN(DE2)
(empty)
DE3
iN(DE3)
(empty)
(empty)
DE3
iN(DE3)
(empty)
(empty)
(empty)
(empty)
iN(DE7)
DE8
(empty)
iN(DE8)
iN(DE7)
12/06/2010
ecs150 fall 2010, final

5. memory disk DE5 DE7 (empty) iN(DE5) (empty) DE7 (empty) iN(DE5)
12/06/2010
ecs150 fall 2010, final

6. The 2nd Sequence – this one is better but why?
memory
disk
DE5
DE7
(empty)
iN(DE5)
(empty)
DE7
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
DE2
(empty)
iN(DE2)
(empty)
DE3
iN(DE3)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
iN(DE7)
DE8
(empty)
iN(DE8)
iN(DE7)
DE5
DE7
(empty)
iN(DE5)
DE7
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
DE3
iN(DE3)
(empty)
(empty)
(empty)
(empty)
(empty)
iN(DE7)
(empty)
DE5
DE7
(empty)
iN(DE5)
iN(DE5)
(empty)
(empty)
(empty)
(empty)
(empty)
(empty)
DE3
iN(DE3)
(empty)
(empty)
(empty)
(empty)
(empty)
iN(DE7)
iN(DE7)
12/06/2010
ecs150 fall 2010, final

7. memory disk DE5 DE7 (empty) iN(DE5) DE5 (empty) (empty) (empty)
12/06/2010
ecs150 fall 2010, final

8. Q-02
Answer: (hint: this question can be answered in just a couple sentences. Please focus on the FIRST block update and explain what’s wrong with that.)
12/06/2010
ecs150 fall 2010, final

9. c-Torrent SnoopFS Q-03 mp3 player 12/06/2010 ecs150 fall 2010, final
(Bit Torrent, V-node, and OS architecture 8%) The following figure shows the relationship among various components of our homework assignment 4. Please describe one main advantage of such an OS/App/Server architecture.
mp3 player
c-Torrent
SnoopFS
12/06/2010
ecs150 fall 2010, final

10. Q-03
(Answer) Hint: please answer this question from the OS kernel architecture point of view. For instance, why shouldn’t the c-torrent client directly obtain the “piece” information from the MP3 player? Why do we bother to use SnoopFS?
12/06/2010
ecs150 fall 2010, final

11. Q-04 2 4 2 1 2 4 5 1 3 3 2 3 1 2 3 2 4 FIFO LRU CLOCK Optimal
(On-demand Paging, 4%) Please complete the following diagrams for FIFO, LRU, CLOCK, and Optimal. And, please remember to put down F in the circles if page faults occur.
Access Reference String: 2 4 2 1 2 4 5 1 3 3 2 3 1 2 3 2 4
FIFO
LRU
CLOCK
Optimal
12/06/2010
ecs150 fall 2010, final

12. Q-05
(Power of 2 Kernel Memory Management, 4%) Please compare FreeBSD’s McKusick-Karels Allocator (MKA) and Linux’s Buddy System (BS) and state one relative strength for each of two. Furthermore, based on the strength and weakness you just describe, please provide two power-of-two memory Allocation/Deallocation patterns such that one pattern will fit very well under MKA but not for BS, and vice versa for another pattern.
12/06/2010
ecs150 fall 2010, final