add related_info on page-replacement-policy algorithms

related_info/lab3/page-replacement-policy.md

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+# 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
+```       

related_info/lab3/page-replacement-policy.py

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+#! /usr/bin/env python
+
+import sys
+from optparse import OptionParser
+import random
+import math
+
+def hfunc(index):
+    if index == -1:
+        return 'MISS'
+    else:
+        return 'HIT '
+
+def vfunc(victim):
+    if victim == -1:
+        return '-'
+    else:
+        return str(victim)
+
+#
+# main program
+#
+parser = OptionParser()
+parser.add_option('-a', '--addresses', default='-1',   help='a set of comma-separated pages to access; -1 means randomly generate',  action='store', type='string', dest='addresses')
+parser.add_option('-p', '--policy', default='FIFO',    help='replacement policy: FIFO, LRU, OPT, CLOCK',                action='store', type='string', dest='policy')
+parser.add_option('-b', '--clockbits', default=1,      help='for CLOCK policy, how many clock bits to use',                          action='store', type='int', dest='clockbits')
+parser.add_option('-f', '--pageframesize', default='3',    help='size of the physical page frame, in pages',                                  action='store', type='string', dest='pageframesize')
+parser.add_option('-s', '--seed', default='0',         help='random number seed',                                                    action='store', type='string', dest='seed')
+parser.add_option('-N', '--notrace', default=False,    help='do not print out a detailed trace',                                     action='store_true', dest='notrace')
+parser.add_option('-c', '--compute', default=False,    help='compute answers for me',                                                action='store_true', dest='solve')
+
+(options, args) = parser.parse_args()
+
+print 'ARG addresses', options.addresses
+print 'ARG policy', options.policy
+print 'ARG clockbits', options.clockbits
+print 'ARG pageframesize', options.pageframesize
+print 'ARG seed', options.seed
+print 'ARG notrace', options.notrace
+print ''
+
+addresses   = str(options.addresses)
+pageframesize   = int(options.pageframesize)
+seed        = int(options.seed)
+policy      = str(options.policy)
+notrace     = options.notrace
+clockbits   = int(options.clockbits)
+
+random.seed(seed)
+
+addrList = []
+addrList = addresses.split(',')
+
+if options.solve == False:
+    print 'Assuming a replacement policy of %s, and a physical page frame of size %d pages,' % (policy, pageframesize)
+    print 'figure out whether each of the following page references hit or miss'
+
+    for n in addrList:
+        print 'Access: %d  Hit/Miss?  State of Memory?' % int(n)
+    print ''
+
+else:
+    if notrace == False:
+        print 'Solving...\n'
+
+    # init memory structure
+    count = 0
+    memory = []
+    hits = 0
+    miss = 0
+
+    if policy == 'FIFO':
+        leftStr = 'FirstIn'
+        riteStr = 'Lastin '
+    elif policy == 'LRU':
+        leftStr = 'LRU'
+        riteStr = 'MRU'
+    elif policy == 'OPT' or  policy == 'CLOCK':
+        leftStr = 'Left '
+        riteStr = 'Right'
+    else:
+        print 'Policy %s is not yet implemented' % policy
+        exit(1)
+
+    # track reference bits for clock
+    ref   = {}
+
+    cdebug = False
+
+    # need to generate addresses
+    addrIndex = 0
+    for nStr in addrList:
+        # first, lookup
+        n = int(nStr)
+        try:
+            idx = memory.index(n)
+            hits = hits + 1
+            if policy == 'LRU' :
+                update = memory.remove(n)
+                memory.append(n) # puts it on MRU side
+        except:
+            idx = -1
+            miss = miss + 1
+
+        victim = -1        
+        if idx == -1:
+            # miss, replace?
+            # print 'BUG count, pageframesize:', count, pageframesize
+            if count == pageframesize:
+                # must replace
+                if policy == 'FIFO' or policy == 'LRU':
+                    victim = memory.pop(0)
+                elif policy == 'CLOCK':
+                    if cdebug:
+                        print 'REFERENCE TO PAGE', n
+                        print 'MEMORY ', memory
+                        print 'REF (b)', ref
+                    # hack: for now, do random
+                    # victim = memory.pop(int(random.random() * count))
+                    victim = -1
+                    while victim == -1:
+                        page = memory[int(random.random() * count)]
+                        if cdebug:
+                            print '  scan page:', page, ref[page]
+                        if ref[page] >= 1:
+                            ref[page] -= 1
+                        else:
+                            # this is our victim
+                            victim = page
+                            memory.remove(page)
+                            break
+
+                    # remove old page's ref count
+                    if page in memory:
+                        assert('BROKEN')
+                    del ref[victim]
+                    if cdebug:
+                        print 'VICTIM', page
+                        print 'LEN', len(memory)
+                        print 'MEM', memory
+                        print 'REF (a)', ref
+
+                elif policy == 'OPT':
+                    maxReplace  = -1
+                    replaceIdx  = -1
+                    replacePage = -1
+                    # print 'OPT: access %d, memory %s' % (n, memory) 
+                    # print 'OPT: replace from FUTURE (%s)' % addrList[addrIndex+1:]
+                    for pageIndex in range(0,count):
+                        page = memory[pageIndex]
+                        # now, have page 'page' at index 'pageIndex' in memory
+                        whenReferenced = len(addrList)
+                        # whenReferenced tells us when, in the future, this was referenced
+                        for futureIdx in range(addrIndex+1,len(addrList)):
+                            futurePage = int(addrList[futureIdx])
+                            if page == futurePage:
+                                whenReferenced = futureIdx
+                                break
+                        # print 'OPT: page %d is referenced at %d' % (page, whenReferenced)
+                        if whenReferenced >= maxReplace:
+                            # print 'OPT: ??? updating maxReplace (%d %d %d)' % (replaceIdx, replacePage, maxReplace)
+                            replaceIdx  = pageIndex
+                            replacePage = page
+                            maxReplace  = whenReferenced
+                            # print 'OPT: --> updating maxReplace (%d %d %d)' % (replaceIdx, replacePage, maxReplace)
+                    victim = memory.pop(replaceIdx)
+                    # print 'OPT: replacing page %d (idx:%d) because I saw it in future at %d' % (victim, replaceIdx, whenReferenced)
+            else:
+                # miss, but no replacement needed (page frame not full)
+                victim = -1
+                count = count + 1
+
+            # now add to memory
+            memory.append(n)
+            if cdebug:
+                print 'LEN (a)', len(memory)
+            if victim != -1:
+                assert(victim not in memory)
+
+        # after miss processing, update reference bit
+        if n not in ref:
+            ref[n] = 1
+        else:
+            ref[n] += 1
+            if ref[n] > clockbits:
+                ref[n] = clockbits
+        
+        if cdebug:
+            print 'REF (a)', ref
+
+        if notrace == False:
+            print 'Access: %d  %s %s -> %12s <- %s Replaced:%s [Hits:%d Misses:%d]' % (n, hfunc(idx), leftStr, memory, riteStr, vfunc(victim), hits, miss)
+        addrIndex = addrIndex + 1
+        
+    print ''
+    print 'FINALSTATS hits %d   misses %d   hitrate %.2f' % (hits, miss, (100.0*float(hits))/(float(hits)+float(miss)))
+    print ''
+
+    
+    
+    
+
+
+
+
+
+
+