Matakuliah
Tahun
Versi/Revisi
: T0316/sistem Operasi
: 2005
:5
Pertemuan 15
Modelling Page Replacement
Algorithm
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• menjelaskan permodelan algoritma pergantian
page dan memprediksi page fault (C2)
2
Outline Materi
•
•
•
•
Belady's Anomali
Stack Algorithm
Distance String
Memprediksi Page fault
3
Modeling Page Replacement Algorithms
Belady's Anomaly
• FIFO with 3 page frames
• FIFO with 4 page frames
• P's show which page references show page faults
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Stack Algorithms
7
4
6 5
State of memory array, M, after each item in reference
string is processed
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Stack Algorithms (2)
…r…
n
m
• Stack algorithm has the property of
M(m, r)  M(m+1, r)
where
•
•
•
•
M  internal array
m  number of page frames
n  virtual pages
r  index into the reference string
 The set of pages included in the top part of M for a memory with m
page frames after r memory references are also included in M for a
memory with m+1 page frames
 LRU has this property but FIFO does not
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 This algorithm do not suffer from Belady’s Anomaly
The Distance String
Probability density functions for two
hypothetical distance strings
7
The Distance String
20
3
17
3
14
3
11
9
1
8
0
• Computation of page fault rate from distance string
– the C vector
– the F vector
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