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-
- This simulator, paging-policy.py, allows you to play around with different
- page-replacement policies. For example, let's examine how LRU performs with a
- series of page references with a cache of size 3:
-
- 0 1 2 0 1 3 0 3 1 2 1
-
- To do so, run the simulator as follows:
-
- prompt> ./paging-policy.py --addresses=0,1,2,0,1,3,0,3,1,2,1
- --policy=LRU --cachesize=3 -c
-
- And what you would see is:
-
- ARG addresses 0,1,2,0,1,3,0,3,1,2,1
- ARG numaddrs 10
- ARG policy LRU
- ARG cachesize 3
- ARG maxpage 10
- ARG seed 0
-
- Solving...
-
- Access: 0 MISS LRU-> [br 0]<-MRU Replace:- [br Hits:0 Misses:1]
- Access: 1 MISS LRU-> [br 0, 1]<-MRU Replace:- [br Hits:0 Misses:2]
- Access: 2 MISS LRU->[br 0, 1, 2]<-MRU Replace:- [br Hits:0 Misses:3]
- Access: 0 HIT LRU->[br 1, 2, 0]<-MRU Replace:- [br Hits:1 Misses:3]
- Access: 1 HIT LRU->[br 2, 0, 1]<-MRU Replace:- [br Hits:2 Misses:3]
- Access: 3 MISS LRU->[br 0, 1, 3]<-MRU Replace:2 [br Hits:2 Misses:4]
- Access: 0 HIT LRU->[br 1, 3, 0]<-MRU Replace:2 [br Hits:3 Misses:4]
- Access: 3 HIT LRU->[br 1, 0, 3]<-MRU Replace:2 [br Hits:4 Misses:4]
- Access: 1 HIT LRU->[br 0, 3, 1]<-MRU Replace:2 [br Hits:5 Misses:4]
- Access: 2 MISS LRU->[br 3, 1, 2]<-MRU Replace:0 [br Hits:5 Misses:5]
- Access: 1 HIT LRU->[br 3, 2, 1]<-MRU Replace:0 [br Hits:6 Misses:5]
- ]
-
- The complete set of possible arguments for paging-policy is listed on the
- following page, and includes a number of options for varying the policy, how
- addresses are specified/generated, and other important parameters such as the
- size of the cache.
-
- prompt> ./paging-policy.py --help
- Usage: paging-policy.py [options]
-
- Options:
- -h, --help show this help message and exit
- -a ADDRESSES, --addresses=ADDRESSES
- a set of comma-separated pages to access;
- -1 means randomly generate
- -f ADDRESSFILE, --addressfile=ADDRESSFILE
- a file with a bunch of addresses in it
- -n NUMADDRS, --numaddrs=NUMADDRS
- if -a (--addresses) is -1, this is the
- number of addrs to generate
- -p POLICY, --policy=POLICY
- replacement policy: FIFO, LRU, LFU, OPT,
- UNOPT, RAND, CLOCK
- -b CLOCKBITS, --clockbits=CLOCKBITS
- for CLOCK policy, how many clock bits to use
- -C CACHESIZE, --cachesize=CACHESIZE
- size of the page cache, in pages
- -m MAXPAGE, --maxpage=MAXPAGE
- if randomly generating page accesses,
- this is the max page number
- -s SEED, --seed=SEED random number seed
- -N, --notrace do not print out a detailed trace
- -c, --compute compute answers for me
- ]
-
- As usual, "-c" is used to solve a particular problem, whereas without it, the
- accesses are just listed (and the program does not tell you whether or not a
- particular access is a hit or miss).
-
- To generate a random problem, instead of using "-a/--addresses" to pass in
- some page references, you can instead pass in "-n/--numaddrs" as the number of
- addresses the program should randomly generate, with "-s/--seed" used to
- specify a different random seed. For example:
-
- prompt> ./paging-policy.py -s 10 -n 3
- .. .
- Assuming a replacement policy of FIFO, and a cache of size 3 pages,
- figure out whether each of the following page references hit or miss
- in the page cache.
-
- Access: 5 Hit/Miss? State of Memory?
- Access: 4 Hit/Miss? State of Memory?
- Access: 5 Hit/Miss? State of Memory?
- ]
-
- As you can see, in this example, we specify "-n 3" which means the program
- should generate 3 random page references, which it does: 5, 7, and 5. The
- random seed is also specified (10), which is what gets us those particular
- numbers. After working this out yourself, have the program solve the problem
- for you by passing in the same arguments but with "-c" (showing just the
- relevant part here):
-
- prompt> ./paging-policy.py -s 10 -n 3 -c
- ...
- Solving...
-
- Access: 5 MISS FirstIn-> [br 5] <-Lastin Replace:- [br Hits:0 Misses:1]
- Access: 4 MISS FirstIn->[br 5, 4] <-Lastin Replace:- [br Hits:0 Misses:2]
- Access: 5 HIT FirstIn->[br 5, 4] <-Lastin Replace:- [br Hits:1 Misses:2]
- ]
-
- The default policy is FIFO, though others are available, including LRU, MRU,
- OPT (the optimal replacement policy, which peeks into the future to see what
- is best to replace), UNOPT (which is the pessimal replacement), RAND (which
- does random replacement), and CLOCK (which does the clock algorithm). The
- CLOCK algorithm also takes another argument (-b), which states how many bits
- should be kept per page; the more clock bits there are, the better the
- algorithm should be at determining which pages to keep in memory.
-
- Other options include: "-C/--cachesize" which changes the size of the page
- cache; "-m/--maxpage" which is the largest page number that will be used if
- the simulator is generating references for you; and "-f/--addressfile" which
- lets you specify a file with addresses in them, in case you wish to get traces
- from a real application or otherwise use a long trace as input.
-
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