47 lines
1.7 KiB
Markdown
47 lines
1.7 KiB
Markdown
|
# 理解页置换算法
|
|||
|
|
## 选择四种替换算法（0：LRU置换算法，1:改进的clock 页置换算法，2：工作集页置换算法，3：缺页率置换算法）中的一种来设计一个应用程序（可基于python, ruby, C, C++，LISP等）模拟实现，并给出测试。请参考page-replacement-policy.py 代码或独自实现。
|
|||
|
|
|
|||
|
|
###page-replacement-policy.py 代码
|
|||
|
|
|
|||
|
|
#### 对模拟环境的抽象
|
|||
|
|
|
|||
|
|
虚拟页访问序列：addresses=1,2,3,4,0,5.... 这里面的最大值代表最大页号
|
|||
|
|
页替换算法：policy=FIFO, LRU, OPT, CLOCK
|
|||
|
|
CLOCK算法用的bit位数：clockbits=1
|
|||
|
|
物理页帧大小：cachesize
|
|||
|
|
实际保持的也访问序列：addrList [1,2,3,4,0,5,...]
|
|||
|
|
物理页帧内容：memory [] 初始为空
|
|||
|
|
当前占用的页帧数量：count 初始位0
|
|||
|
|
|
|||
|
|
#### 执行过程描述
|
|||
|
|
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
for nStr in addrList:
|
|||
|
|
# for clock need to track the ref by reference bits
|
|||
|
|
|
|||
|
|
try:
|
|||
|
|
idx = memory.index(n)
|
|||
|
|
hits = hits + 1
|
|||
|
|
if policy == 'LRU' :
|
|||
|
|
....
|
|||
|
|
except:
|
|||
|
|
idx = -1 #missing
|
|||
|
|
miss = miss + 1
|
|||
|
|
|
|||
|
|
if idx=-1 and ...: #missing and need replacement
|
|||
|
|
#if phy page frames are full
|
|||
|
|
# for FIFO , LRU
|
|||
|
|
# replace victim item from memory by " victim = memory.pop(0)"
|
|||
|
|
|
|||
|
|
# for CLOCK
|
|||
|
|
# find one page for the beginning of scan
|
|||
|
|
# check ref[page] and update ref[page]
|
|||
|
|
# find a victim which ref[page]=0 by memory.remove(page)
|
|||
|
|
else:
|
|||
|
|
# miss, but no replacement needed (phy page frame not full)
|
|||
|
|
# now add to memory
|
|||
|
|
|
|||
|
|
#update ref for clock replacement
|
|||
|
|
```
|