命 中 率 = 1 − 页 面 失 效 次 数 页 地 址 流 长 度 命中率=1-\frac{页面失效次数}{页地址流长度} 命中率=1−页地址流长度页面失效次数
页面调度算法
- LRU：当需要淘汰一个页面时，总是选择在最近一段时间内最久不用的页面予以淘汰。
- FIFO：当需要淘汰一个页面时，总是选择驻留主存时间最长的页面进行淘汰，即先进入主存的页面先淘汰。
- LFU：总是淘汰最近一段时间内使用次数很少的页面。
- Opt：从主存中移出永远不再需要的页面；如无这样的页面存在，则选择最长时间不需要访问的页面。
代码
总共10页。四个块，程序要30次调用页，的页号序列随机在指定。
# -*- coding: utf-8 -*-
# 运行python3.7.8
import time
import sys
import random
from multiprocessing import *
class Page:
'''
页面。
'''
def __init__(self, index: int):
'''
初始化页面。
参数
--------
index : int
页序号。
'''
self.__index = index
self.__pv = 0
self.__last_visit = float(time.time()) # 时间戳
self.__last_put = -1 # 上次装入时间
pass
@property
def pv(self):
'''
访问次数。
'''
return self.__pv
@property
def last_visit(self):
'''
访问时间。
'''
return self.__last_visit
def visit(self):
self.__pv += 1
time.sleep(0.001)
self.__last_visit = float(time.time()) # 时间戳
@property
def index(self):
'''
页号。
'''
return self.__index
def set_last_put(self):
self.__last_put = float(time.time())
pass
@property
def last_put(self):
return self.__last_put
class Mem:
'''
为进程申请的独立内存空间。
'''
def __init__(self, size: int, func):
'''
初始化内存。
参数
--------
size : int
以页为单位的内存容量。
func
页面置换算法，必需传入名为page、blocks的参数，并返回一个页。
'''
self.__blocks = []
self.__max_size = size
self.__func = func
self.__find = 0
self.__total = 0
pass
@property
def max(self):
'''
以页为单位的内存容量。
'''
return self.__max_size
@property
def size(self):
'''
已使用页数。
'''
return len(self.__blocks)
def print_mem(self):
'''
打印占页情况。
'''
print('[ ', end='')
first = True
length = len(self.__blocks)
for i in range(0, self.__max_size):
if i < length:
if first:
print(str(self.__blocks[i].index).zfill(2), end='')
first = False
else:
print('\t | ' + str(self.__blocks[i].index).zfill(2), end='')
pass
else:
if first:
print(' ', end='')
first = False
else:
print('\t | '+'-', end='')
pass
print('\t]')
pass
def get(self, index):
'''
查看已经使用的页。
'''
if index > 0 and index < self.__size:
return self.__blocks[index]
else:
return None
pass
def push(self, page: Page):
'''
装入页面。
参数
--------
page : Page
待装入页面。
'''
try:
for i in self.__blocks:
if page.index == i.index:
i.visit()
self.__find += 1
self.__total += 1
return
index = None
if self.size < self.max:
self.__blocks.append(page)
self.__total += 1
page.visit()
page.set_last_put()
return
else:
rem = self.__func(page=page, blocks=self.__blocks)
if rem is not None:
for i in self.__blocks:
if i.index is rem.index:
index = self.__blocks.index(i)
break
pass
if index is not None:
self.__blocks[index] = page
self.__total += 1
page.visit()
page.set_last_put()
pass
except BaseException as e:
print(repr(e))
pass
else:
pass
pass
@property
def pfr(self):
ret = 1-self.hr # 缺页率
return ret
@property
def hr(self):
ret = self.__find/self.__total # 命中率
return ret
all_pages = []
all_indexs = []
now_index = 0
def run(func, size: int, page_count: int):
try:
global all_pages
global now_index
all_pages = []
now_index = 0
for i in range(0, page_count):
all_pages.append(Page(i)) # 初始化内存
pass
mem = Mem(size, func)
for index in all_indexs:
now_index += 1 # 为Opt服务
print('('+str(now_index).zfill(3)+')\t: ',end='')
i = all_pages[index]
mem.push(i) # 初始化模拟进程
print(str(i.index).zfill(2), end='\t--> ')
mem.print_mem()
pass
print('-'*16)
print('Hit rate: ' + str(mem.hr))
print('Page fault rate: '+str(mem.pfr))
print('-'*16+'\n')
pass
except Exception as e:
e.print_exc()
pass
else:
pass
pass
def LRU(page: Page, blocks: list):
'''
最久未使用。
'''
ret = None
min = sys.float_info.max
for i in blocks:
if i != None:
if i.last_visit < min:
ret = i
min = i.last_visit
return ret
def FIFO(page: Page, blocks: list):
'''
先进先出。
'''
ret = None
min = sys.float_info.max
for i in blocks:
if i != None:
if i.last_put < min:
ret = i
min = i.last_put
return ret
def LFU(page: Page, blocks: list):
'''
最少使用。
'''
ret = None
min = sys.maxsize
for i in blocks:
if i != None:
if i.pv < min:
ret = i
min = i.pv
return ret
def Opt(page: Page, blocks: list):
'''
最佳。
'''
global all_pages
global now_index
ret = None
max = 0
for i in blocks:
if i != None:
d = 0
for future in range(now_index, len(all_indexs)):
if all_indexs[future] == i.index:
break
d += 1
pass
if d > max:
ret = i
max = d
return ret
def __main__():
page_count=10
global all_indexs
for i in range(0, 30): # 进程所需页号
all_indexs.append(random.randint(1, page_count)-1)
pass
print('-'*16+'\n'+'LRU:')
run(LRU, 4, page_count)
print('-'*16+'\n'+'FIFO:')
run(FIFO, 4, page_count)
print('-'*16+'\n'+'LFU:')
run(LFU, 4, page_count)
print('-'*16+'\n'+'Opt:')
run(Opt, 4, page_count)
pass
__main__()
运行结果
----------------
LRU:
(001) : 07 --> [ 07 | - | - | - ]
(002) : 05 --> [ 07 | 05 | - | - ]
(003) : 03 --> [ 07 | 05 | 03 | - ]
(004) : 00 --> [ 07 | 05 | 03 | 00 ]
(005) : 06 --> [ 06 | 05 | 03 | 00 ]
(006) : 08 --> [ 06 | 08 | 03 | 00 ]
(007) : 09 --> [ 06 | 08 | 09 | 00 ]
(008) : 01 --> [ 06 | 08 | 09 | 01 ]
(009) : 05 --> [ 05 | 08 | 09 | 01 ]
(010) : 01 --> [ 05 | 08 | 09 | 01 ]
(011) : 00 --> [ 05 | 00 | 09 | 01 ]
(012) : 03 --> [ 05 | 00 | 03 | 01 ]
(013) : 05 --> [ 05 | 00 | 03 | 01 ]
(014) : 09 --> [ 05 | 00 | 03 | 09 ]
(015) : 08 --> [ 05 | 08 | 03 | 09 ]
(016) : 04 --> [ 05 | 08 | 04 | 09 ]
(017) : 09 --> [ 05 | 08 | 04 | 09 ]
(018) : 01 --> [ 01 | 08 | 04 | 09 ]
(019) : 06 --> [ 01 | 06 | 04 | 09 ]
(020) : 02 --> [ 01 | 06 | 02 | 09 ]
(021) : 06 --> [ 01 | 06 | 02 | 09 ]
(022) : 03 --> [ 01 | 06 | 02 | 03 ]
(023) : 00 --> [ 00 | 06 | 02 | 03 ]
(024) : 09 --> [ 00 | 06 | 09 | 03 ]
(025) : 05 --> [ 00 | 05 | 09 | 03 ]
(026) : 03 --> [ 00 | 05 | 09 | 03 ]
(027) : 05 --> [ 00 | 05 | 09 | 03 ]
(028) : 08 --> [ 08 | 05 | 09 | 03 ]
(029) : 02 --> [ 08 | 05 | 02 | 03 ]
(030) : 06 --> [ 08 | 05 | 02 | 06 ]
----------------
Hit rate: 0.2
Page fault rate: 0.8
----------------
----------------
FIFO:
(001) : 07 --> [ 07 | - | - | - ]
(002) : 05 --> [ 07 | 05 | - | - ]
(003) : 03 --> [ 07 | 05 | 03 | - ]
(004) : 00 --> [ 07 | 05 | 03 | 00 ]
(005) : 06 --> [ 06 | 05 | 03 | 00 ]
(006) : 08 --> [ 06 | 08 | 03 | 00 ]
(007) : 09 --> [ 06 | 08 | 09 | 00 ]
(008) : 01 --> [ 06 | 08 | 09 | 01 ]
(009) : 05 --> [ 05 | 08 | 09 | 01 ]
(010) : 01 --> [ 05 | 08 | 09 | 01 ]
(011) : 00 --> [ 05 | 00 | 09 | 01 ]
(012) : 03 --> [ 05 | 00 | 03 | 01 ]
(013) : 05 --> [ 05 | 00 | 03 | 01 ]
(014) : 09 --> [ 05 | 00 | 03 | 09 ]
(015) : 08 --> [ 08 | 00 | 03 | 09 ]
(016) : 04 --> [ 08 | 04 | 03 | 09 ]
(017) : 09 --> [ 08 | 04 | 03 | 09 ]
(018) : 01 --> [ 08 | 04 | 01 | 09 ]
(019) : 06 --> [ 08 | 04 | 01 | 06 ]
(020) : 02 --> [ 02 | 04 | 01 | 06 ]
(021) : 06 --> [ 02 | 04 | 01 | 06 ]
(022) : 03 --> [ 02 | 03 | 01 | 06 ]
(023) : 00 --> [ 02 | 03 | 00 | 06 ]
(024) : 09 --> [ 02 | 03 | 00 | 09 ]
(025) : 05 --> [ 05 | 03 | 00 | 09 ]
(026) : 03 --> [ 05 | 03 | 00 | 09 ]
(027) : 05 --> [ 05 | 03 | 00 | 09 ]
(028) : 08 --> [ 05 | 08 | 00 | 09 ]
(029) : 02 --> [ 05 | 08 | 02 | 09 ]
(030) : 06 --> [ 05 | 08 | 02 | 06 ]
----------------
Hit rate: 0.2
Page fault rate: 0.8
----------------
----------------
LFU:
(001) : 07 --> [ 07 | - | - | - ]
(002) : 05 --> [ 07 | 05 | - | - ]
(003) : 03 --> [ 07 | 05 | 03 | - ]
(004) : 00 --> [ 07 | 05 | 03 | 00 ]
(005) : 06 --> [ 06 | 05 | 03 | 00 ]
(006) : 08 --> [ 08 | 05 | 03 | 00 ]
(007) : 09 --> [ 09 | 05 | 03 | 00 ]
(008) : 01 --> [ 01 | 05 | 03 | 00 ]
(009) : 05 --> [ 01 | 05 | 03 | 00 ]
(010) : 01 --> [ 01 | 05 | 03 | 00 ]
(011) : 00 --> [ 01 | 05 | 03 | 00 ]
(012) : 03 --> [ 01 | 05 | 03 | 00 ]
(013) : 05 --> [ 01 | 05 | 03 | 00 ]
(014) : 09 --> [ 09 | 05 | 03 | 00 ]
(015) : 08 --> [ 08 | 05 | 03 | 00 ]
(016) : 04 --> [ 04 | 05 | 03 | 00 ]
(017) : 09 --> [ 09 | 05 | 03 | 00 ]
(018) : 01 --> [ 09 | 05 | 01 | 00 ]
(019) : 06 --> [ 09 | 05 | 01 | 06 ]
(020) : 02 --> [ 09 | 05 | 01 | 02 ]
(021) : 06 --> [ 09 | 05 | 01 | 06 ]
(022) : 03 --> [ 03 | 05 | 01 | 06 ]
(023) : 00 --> [ 00 | 05 | 01 | 06 ]
(024) : 09 --> [ 09 | 05 | 01 | 06 ]
(025) : 05 --> [ 09 | 05 | 01 | 06 ]
(026) : 03 --> [ 09 | 05 | 03 | 06 ]
(027) : 05 --> [ 09 | 05 | 03 | 06 ]
(028) : 08 --> [ 09 | 05 | 03 | 08 ]
(029) : 02 --> [ 09 | 05 | 03 | 02 ]
(030) : 06 --> [ 09 | 05 | 03 | 06 ]
----------------
Hit rate: 0.23333333333333334
Page fault rate: 0.7666666666666666
----------------
----------------
Opt:
(001) : 07 --> [ 07 | - | - | - ]
(002) : 05 --> [ 07 | 05 | - | - ]
(003) : 03 --> [ 07 | 05 | 03 | - ]
(004) : 00 --> [ 07 | 05 | 03 | 00 ]
(005) : 06 --> [ 06 | 05 | 03 | 00 ]
(006) : 08 --> [ 08 | 05 | 03 | 00 ]
(007) : 09 --> [ 09 | 05 | 03 | 00 ]
(008) : 01 --> [ 01 | 05 | 03 | 00 ]
(009) : 05 --> [ 01 | 05 | 03 | 00 ]
(010) : 01 --> [ 01 | 05 | 03 | 00 ]
(011) : 00 --> [ 01 | 05 | 03 | 00 ]
(012) : 03 --> [ 01 | 05 | 03 | 00 ]
(013) : 05 --> [ 01 | 05 | 03 | 00 ]
(014) : 09 --> [ 01 | 09 | 03 | 00 ]
(015) : 08 --> [ 01 | 09 | 03 | 08 ]
(016) : 04 --> [ 01 | 09 | 03 | 04 ]
(017) : 09 --> [ 01 | 09 | 03 | 04 ]
(018) : 01 --> [ 01 | 09 | 03 | 04 ]
(019) : 06 --> [ 06 | 09 | 03 | 04 ]
(020) : 02 --> [ 06 | 09 | 03 | 02 ]
(021) : 06 --> [ 06 | 09 | 03 | 02 ]
(022) : 03 --> [ 06 | 09 | 03 | 02 ]
(023) : 00 --> [ 00 | 09 | 03 | 02 ]
(024) : 09 --> [ 00 | 09 | 03 | 02 ]
(025) : 05 --> [ 05 | 09 | 03 | 02 ]
(026) : 03 --> [ 05 | 09 | 03 | 02 ]
(027) : 05 --> [ 05 | 09 | 03 | 02 ]
(028) : 08 --> [ 08 | 09 | 03 | 02 ]
(029) : 02 --> [ 08 | 09 | 03 | 02 ]
(030) : 06 --> [ 08 | 09 | 03 | 02 ]
----------------
Hit rate: 0.4482758620689655
Page fault rate: 0.5517241379310345
----------------