47 lines
1.7 KiB
Markdown
47 lines
1.7 KiB
Markdown
# 理解页置换算法
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## 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。
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###page-replacement-policy.py 代码
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#### 对模拟环境的抽象
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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
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页替换算法：policy=FIFO, LRU, OPT, CLOCK
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CLOCK算法用的bit位数：clockbits=1
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物理页帧大小：cachesize
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实际保持的也访问序列：addrList [1,2,3,4,0,5,...]
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物理页帧内容：memory [] 初始为空
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当前占用的页帧数量：count 初始位0
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#### 执行过程描述
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```
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for nStr in addrList:
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# for clock need to track the ref by reference bits
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try:
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idx = memory.index(n)
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hits = hits + 1
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if policy == 'LRU' :
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....
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except:
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idx = -1 #missing
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miss = miss + 1
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if idx=-1 and ...: #missing and need replacement
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#if phy page frames are full
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# for FIFO , LRU
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# replace victim item from memory by " victim = memory.pop(0)"
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# for CLOCK
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# find one page for the beginning of scan
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# check ref[page] and update ref[page]
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# find a victim which ref[page]=0 by memory.remove(page)
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else:
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# miss, but no replacement needed (phy page frame not full)
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# now add to memory
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#update ref for clock replacement
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```
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