[python]实现操作系统虚拟内存中的页替换算法FIFO,OPT,LRU

OPT：最佳替换算法（optional
replacement）。替换下次访问距当前时间最长的页。

LRU:最近最少使用(Least Recently Used).替换上次使用距离当前最远的页。

FIFO:先进先出(First
In First Out),将页面看做一个循环缓冲区，按循环方式替换。这是实现最为简单的算法，隐含的逻辑是替换驻留在内存时间最长的页。

FIFO:

BLOCKNUMBER = 3

#加载数据
def loadData():
F = open('data')
data = F.read().split(' ')
F.close()
return data

usedBlock = []
n = 0

# 将下一页加入到内存中
def loadNextPage(memory,page):
global n

if page not in memory:
n += 1
if len(memory)<BLOCKNUMBER:
memory.append(page)
else:
memory.pop(0)
memory.append(page)

return memory

data = loadData()
for i in data:
usedBlock = loadNextPage(usedBlock,i)
# print(usedBlock)

print('发生缺页的次数为%s' %n)


OPT:

BLOCKNUMBER = 3

#加载数据
def loadData():
F = open('data')
data = F.read().split(' ')
F.close()
return data

usedBlock = []
n = 0

def loadNextPage(memory,page,data):
global n
l = []
if page not in memory:
n += 1
if len(memory) < BLOCKNUMBER:
memory.append(page)

else:
for m in memory:
for i in range(len(data)):
if m == data[i]:
l.append(i)
break
elif i == len(data)-1 and m != data[i]:
l.append(2147483647)
index = l.index(max(l))

memory.remove(memory[index])
memory.append(page)
return memory

data = loadData()
data2 = data.copy()
for i in data:
data2.remove(i)
usedBlock = loadNextPage(usedBlock,i,data2)

print('发生缺页的次数为%s' %n)



LRU:

BLOCKNUMBER = 3

#加载数据
def loadData():
F = open('data')
data = F.read().split(' ')
F.close()
return data

usedBlock = []
n = 0

def loadNextPage(memory,page):
global n

if page in memory:
memory.remove(page)
memory.append(page)
else:
n += 1
if len(memory)<BLOCKNUMBER:
memory.append(page)
else:
memory.pop(0)
memory.append(page)
return memory

data = loadData()
for i in data:
usedBlock = loadNextPage(usedBlock,i)

print('发生缺页的次数
4000
为%s' %n)