实战式页式内存管理
课程设计目标(Qt下实现)
1.用代码描述:页表,页框表,任务结构
2.用代码实现:页请求,页置换
3.模拟任务的页面访问过程(访问虚拟内存)
4.模拟操作系统中的任务调度(扩展)
实现的关键点
1.页框表是全局唯一的,用于记录内存页使用情况
2.页表是任务私有的,用于记录虚拟页到内存页的映射关系
3.每一个任务需要一个结构体进行表示
实现关键点
1.页框分配操作:int GetFrameItem()
2.页请求操作:int RequestPage(int pid,int page)
3.页交换操作:int SwapPage()
实现关键点
在实现页式内存管理时,如何模拟不同的任务?可以根据不同任务的虚拟页访问顺序不同,产生页面访问序列
实现的流程图如下所示
代码实现
#include <QtCore/QCoreApplication>
#include <QList>
#include <iostream>
#include <ctime>
using namespace std;
//全局定义的页框表 页表
#define PAGE_NUM (0xFF + 1)
#define FRAME_NUM (0x04)
#define FP_NONE (-1)
struct FrameItem//页框表
{
int pid; // the task which use the frame
int pnum; // the page which the frame hold
FrameItem()
{
pid = FP_NONE;
pnum = FP_NONE;
}
};
class PageTable//页表
{
int m_pt[PAGE_NUM];
public:
PageTable()
{
for(int i=0; i<PAGE_NUM; i++)
{
m_pt[i] = FP_NONE;
}
}
int& operator[] (int i)
{
if( (0 <= i) && (i < length()) )
{
return m_pt[i];
}
else
{
QCoreApplication::exit(-1);
}
}
int length()
{
return PAGE_NUM;
}
};
class PCB
{
int m_pid; // task id
PageTable m_pageTable; // page table for the task
int* m_pageSerial; // simulate the page serial access
int m_pageSerialCount; // page access count
int m_next; // the next page index to access
public:
PCB(int pid)
{
m_pid = pid;
m_pageSerialCount = qrand() % 5 + 5;
m_pageSerial = new int[m_pageSerialCount];
for(int i=0; i<m_pageSerialCount; i++)
{
m_pageSerial[i] = qrand() % 8;
}
m_next = 0;
}
int getPID()
{
return m_pid;
}
PageTable& getPageTable()
{
return m_pageTable;
}
int getNextPage()
{
int ret = m_next++;
if( ret < m_pageSerialCount )
{
ret = m_pageSerial[ret];
}
else
{
ret = FP_NONE;
}
return ret;
}
bool running()
{
return (m_next < m_pageSerialCount);
}
void printPageSerial()
{
QString s = "";
for(int i=0; i<m_pageSerialCount; i++)
{
s += QString::number(m_pageSerial[i]) + " ";
}
cout << ("Task" + QString::number(m_pid) + " : " + s).toStdString() << endl;
}
~PCB()
{
delete[] m_pageSerial;
}
};
FrameItem FrameTable[FRAME_NUM];
QList<PCB*> TaskTable;
int GetFrameItem();
void AccessPage(PCB& pcb);
int RequestPage(int pid, int page);
int SwapPage();
//打印函数的实现
void PrintLog(QString log);
void PrintPageMap(int pid, int page, int frame);
void PrintFatalError(QString s, int pid, int page);
int GetFrameItem()
{
int ret = FP_NONE;
for(int i=0; i<FRAME_NUM; i++)
{
if( FrameTable[i].pid == FP_NONE )
{
ret = i;
break;
}
}
return ret;
}
void AccessPage(PCB& pcb)
{
int pid = pcb.getPID();
PageTable& pageTable = pcb.getPageTable();
int page = pcb.getNextPage();
if( page != FP_NONE )
{
PrintLog("Access Task" + QString::number(pid) + " for Page" + QString::number(page));
if( pageTable[page] != FP_NONE )
{
PrintLog("Find target page in page table.");
PrintPageMap(pid, page, pageTable[page]);
}
else
{
PrintLog("Target page is NOT found, need to request page ...");
pageTable[page] = RequestPage(pid, page);
if( pageTable[page] != FP_NONE )
{
PrintPageMap(pid, page, pageTable[page]);
}
else
{
PrintFatalError("Can NOT request page from disk...", pid, page);
}
}
}
else
{
PrintLog("Task" + QString::number(pid) + " is finished!");
}
}
int RequestPage(int pid, int page)
{
int frame = GetFrameItem();
if( frame != FP_NONE )
{
PrintLog("Get a frame to hold page content: Frame" + QString::number(frame));
}
else
{
PrintLog("No free frame to allocate, need to swap page out.");
frame = SwapPage();
if( frame != FP_NONE )
{
PrintLog("Succeed to swap lazy page out.");
}
else
{
PrintFatalError("Failed to swap page out.", pid, FP_NONE);
}
}
PrintLog("Load content from disk to Frame" + QString::number(frame));
FrameTable[frame].pid = pid;
FrameTable[frame].pnum = page;
return frame;
}
//随机生成的实现
int Random()
{
// just random select
int obj = qrand() % FRAME_NUM;
PrintLog("Random select a frame to swap page content out: Frame" + QString::number(obj));
PrintLog("Write the selected page content back to disk.");
FrameTable[obj].pid = FP_NONE;
FrameTable[obj].pnum = FP_NONE;
for(int i=0, f=0; (i<TaskTable.count()) && !f; i++)
{
PageTable& pt = TaskTable[i]->getPageTable();
for(int j=0; j<pt.length(); j++)
{
if( pt[j] == obj )
{
pt[j] = FP_NONE;
f = 1;
break;
}
}
}
return obj;
}
int SwapPage()
{
return Random();
}
void PrintLog(QString log)
{
cout << log.toStdString() << endl;
}
void PrintPageMap(int pid, int page, int frame)
{
QString s = "Task" + QString::number(pid) + " : ";
s += "Page" + QString::number(page) + " ==> Frame" + QString::number(frame);
cout << s.toStdString() << endl;
}
void PrintFatalError(QString s, int pid, int page)
{
s += " Task" + QString::number(pid) + ": Page" + QString::number(page);
cout << s.toStdString() << endl;
QCoreApplication::exit(-2);
}
//实现
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
int index = 0;
qsrand(time(NULL));
TaskTable.append(new PCB(1));
PrintLog("Task Page Serial:");
for(int i=0; i<TaskTable.count(); i++)
{
TaskTable[i]->printPageSerial();
}
PrintLog("==== Running ====");
while( true )
{
if( TaskTable[index]->running() )
{
AccessPage(*TaskTable[index]);
}
index = (index + 1) % TaskTable.count();
cin.get();
}
return a.exec();
}
实现结果
从程序运行结果中可以看到,随机生成了5个页面,在程序定义的时候定义了四个页面框,在程序运行的时候可以看到前面四个页面2 5 6 1分别与四个页框有了一一对应的映射关系,当运行到页面7时,发现页框用完,需要重新申请,这个时候随机将页框2中的页面进行交换,将页面7进行插入
实战页式内存管理中
课程设计目标
1.处理运行结束的任务
2.实现FIFO页面交换的算法
3.实现LRU页面交换算法
目标一
1.将任务结构从任务表中移除
2.回收任务所使用的页框
3.释放任务结构所占的内存
目标二-实现FIFO页交换算法
原理:利用队列(Qt)记录页框使用的时间,页框是在队列中排序的,在交换时将最先进入队列的页框移除
过程:申请队列,页请求时请求成功,将对应的页框号加入到队列尾部,在进行页请求时,没有空余的页框,需要进行页交换,将头部的队列页框移出队列
代码实现
#include <QtCore/QCoreApplication>
#include <QList>
#include <QQueue>
#include <iostream>
#include <ctime>
using namespace std;
#define PAGE_NUM (0xFF + 1)
#define FRAME_NUM (0x04)
#define FP_NONE (-1)
struct FrameItem
{
int pid; // the task which use the frame
int pnum; // the page which the frame hold
int ticks; // the ticks to mark the usage frequency
FrameItem()
{
pid = FP_NONE;
pnum = FP_NONE;
ticks = 0xFF;
}
};
class PageTable
{
int m_pt[PAGE_NUM];
public:
PageTable()
{
for(int i=0; i<PAGE_NUM; i++)
{
m_pt[i] = FP_NONE;
}
}
int& operator[] (int i)
{
if( (0 <= i) && (i < length()) )
{
return m_pt[i];
}
else
{
QCoreApplication::exit(-1);
return m_pt[0]; // for avoid warning
}
}
int length()
{
return PAGE_NUM;
}
};
class PCB
{
int m_pid; // task id
PageTable m_pageTable; // page table for the task
int* m_pageSerial; // simulate the page serial access
int m_pageSerialCount; // page access count
int m_next; // the next page index to access
public:
PCB(int pid)
{
m_pid = pid;
m_pageSerialCount = qrand() % 5 + 5;
m_pageSerial = new int[m_pageSerialCount];
for(int i=0; i<m_pageSerialCount; i++)
{
m_pageSerial[i] = qrand() % 8;
}
m_next = 0;
}
int getPID()
{
return m_pid;
}
PageTable& getPageTable()
{
return m_pageTable;
}
int getNextPage()
{
int ret = m_next++;
if( ret < m_pageSerialCount )
{
ret = m_pageSerial[ret];
}
else
{
ret = FP_NONE;
}
return ret;
}
bool running()
{
return (m_next < m_pageSerialCount);
}
void printPageSerial()
{
QString s = "";
for(int i=0; i<m_pageSerialCount; i++)
{
s += QString::number(m_pageSerial[i]) + " ";
}
cout << ("Task" + QString::number(m_pid) + " : " + s).toStdString() << endl;
}
~PCB()
{
delete[] m_pageSerial;
}
};
FrameItem FrameTable[FRAME_NUM];
QList<PCB*> TaskTable;
QQueue<int> MoveOut;
int GetFrameItem();
void AccessPage(PCB& pcb);
int RequestPage(int pid, int page);
int SwapPage();
void ClearFrameItem(PCB& pcb);
void ClearFrameItem(int frame);
int Random();
int FIFO();
int LRU();
void PrintLog(QString log);
void PrintPageMap(int pid, int page, int frame);
void PrintFatalError(QString s, int pid, int page);
int GetFrameItem()
{
int ret = FP_NONE;
for(int i=0; i<FRAME_NUM; i++)
{
if( FrameTable[i].pid == FP_NONE )
{
ret = i;
break;
}
}
return ret;
}
void AccessPage(PCB& pcb)
{
int pid = pcb.getPID();
PageTable& pageTable = pcb.getPageTable();
int page = pcb.getNextPage();
if( page != FP_NONE )
{
PrintLog("Access Task" + QString::number(pid) + " for Page" + QString::number(page));
if( pageTable[page] != FP_NONE )
{
PrintLog("Find target page in page table.");
PrintPageMap(pid, page, pageTable[page]);
}
else
{
PrintLog("Target page is NOT found, need to request page ...");
pageTable[page] = RequestPage(pid, page);
if( pageTable[page] != FP_NONE )
{
PrintPageMap(pid, page, pageTable[page]);
}
else
{
PrintFatalError("Can NOT request page from disk...", pid, page);
}
}
FrameTable[pageTable[page]].ticks++;
}
else
{
PrintLog("Task" + QString::number(pid) + " is finished!");
}
}
int RequestPage(int pid, int page)
{
int frame = GetFrameItem();
if( frame != FP_NONE )
{
PrintLog("Get a frame to hold page content: Frame" + QString::number(frame));
}
else
{
PrintLog("No free frame to allocate, need to swap page out.");
frame = SwapPage();
if( frame != FP_NONE )
{
PrintLog("Succeed to swap lazy page out.");
}
else
{
PrintFatalError("Failed to swap page out.", pid, FP_NONE);
}
}
PrintLog("Load content from disk to Frame" + QString::number(frame));
FrameTable[frame].pid = pid;
FrameTable[frame].pnum = page;
FrameTable[frame].ticks = 0xFF;
MoveOut.enqueue(frame);//将页框号进行插入
return frame;
}
void ClearFrameItem(int frame)
{
FrameTable[frame].pid = FP_NONE;
FrameTable[frame].pnum = FP_NONE;
for(int i=0, f=0; (i<TaskTable.count()) && !f; i++)
{
PageTable& pt = TaskTable[i]->getPageTable();
for(int j=0; j<pt.length(); j++)
{
if( pt[j] == frame )
{
pt[j] = FP_NONE;
f = 1;
break;
}
}
}
}
int Random()
{
// just random select
int obj = qrand() % FRAME_NUM;
PrintLog("Random select a frame to swap page content out: Frame" + QString::number(obj));
PrintLog("Write the selected page content back to disk.");
ClearFrameItem(obj);
return obj;
}
int FIFO()//FIFO的实现
{
// select the first page in memory to move out
int obj = MoveOut.dequeue();//出队列的操作
PrintLog("Select a frame to swap page content out: Frame" + QString::number(obj));
PrintLog("Write the selected page content back to disk.");
ClearFrameItem(obj);
return obj;
}
int LRU()
{
int obj = 0;
int ticks = FrameTable[obj].ticks;
QString s = "";
for(int i=0; i<FRAME_NUM; i++)
{
s += "Frame" + QString::number(i) + " : " + QString::number(FrameTable[i].ticks) + " ";
if( ticks > FrameTable[i].ticks )
{
ticks = FrameTable[i].ticks;
obj = i;
}
}
PrintLog(s);
PrintLog("Select the LRU frame page to swap content out: Frame" + QString::number(obj));
PrintLog("Write the selected page content back to disk.");
return obj;
}
int SwapPage()
{
return FIFO();
}
void ClearFrameItem(PCB& pcb)
{
for(int i=0; i<FRAME_NUM; i++)
{
if( FrameTable[i].pid == pcb.getPID() )
{
FrameTable[i].pid = FP_NONE;
FrameTable[i].pnum = FP_NONE;
}
}
}
void PrintLog(QString log)
{
cout << log.toStdString() << endl;
}
void PrintPageMap(int pid, int page, int frame)
{
QString s = "Task" + QString::number(pid) + " : ";
s += "Page" + QString::number(page) + " ==> Frame" + QString::number(frame);
cout << s.toStdString() << endl;
}
void PrintFatalError(QString s, int pid, int page)
{
s += " Task" + QString::number(pid) + ": Page" + QString::number(page);
cout << s.toStdString() << endl;
QCoreApplication::exit(-2);
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
int index = 0;
qsrand(time(NULL));
TaskTable.append(new PCB(1));
PrintLog("Task Page Serial:");
for(int i=0; i<TaskTable.count(); i++)
{
TaskTable[i]->printPageSerial();
}
PrintLog("==== Running ====");
while( true )
{
if( TaskTable[index]->running() )
{
AccessPage(*TaskTable[index]);
}
index = (index + 1) % TaskTable.count();
cin.get();
}
return a.exec();
}
实现结果
从实验结果可以看到,随机生成了页面,在进行页请求交换是,是按照队列将队列头部进行移出的
目标三-实现LRU页交换算法
代码实现
#include <QtCore/QCoreApplication>
#include <QList>
#include <QQueue>
#include <iostream>
#include <ctime>
using namespace std;
#define PAGE_NUM (0xFF + 1)
#define FRAME_NUM (0x04)
#define FP_NONE (-1)
struct FrameItem
{
int pid; // the task which use the frame
int pnum; // the page which the frame hold
int ticks; // the ticks to mark the usage frequency
FrameItem()
{
pid = FP_NONE;
pnum = FP_NONE;
ticks = 0xFF;
}
};
class PageTable
{
int m_pt[PAGE_NUM];
public:
PageTable()
{
for(int i=0; i<PAGE_NUM; i++)
{
m_pt[i] = FP_NONE;
}
}
int& operator[] (int i)
{
if( (0 <= i) && (i < length()) )
{
return m_pt[i];
}
else
{
QCoreApplication::exit(-1);
return m_pt[0]; // for avoid warning
}
}
int length()
{
return PAGE_NUM;
}
};
class PCB
{
int m_pid; // task id
PageTable m_pageTable; // page table for the task
int* m_pageSerial; // simulate the page serial access
int m_pageSerialCount; // page access count
int m_next; // the next page index to access
public:
PCB(int pid)
{
m_pid = pid;
m_pageSerialCount = qrand() % 5 + 5;
m_pageSerial = new int[m_pageSerialCount];
for(int i=0; i<m_pageSerialCount; i++)
{
m_pageSerial[i] = qrand() % 8;
}
m_next = 0;
}
int getPID()
{
return m_pid;
}
PageTable& getPageTable()
{
return m_pageTable;
}
int getNextPage()
{
int ret = m_next++;
if( ret < m_pageSerialCount )
{
ret = m_pageSerial[ret];
}
else
{
ret = FP_NONE;
}
return ret;
}
bool running()
{
return (m_next < m_pageSerialCount);
}
void printPageSerial()
{
QString s = "";
for(int i=0; i<m_pageSerialCount; i++)
{
s += QString::number(m_pageSerial[i]) + " ";
}
cout << ("Task" + QString::number(m_pid) + " : " + s).toStdString() << endl;
}
~PCB()
{
delete[] m_pageSerial;
}
};
FrameItem FrameTable[FRAME_NUM];
QList<PCB*> TaskTable;
QQueue<int> MoveOut;
int GetFrameItem();
void AccessPage(PCB& pcb);
int RequestPage(int pid, int page);
int SwapPage();
void ClearFrameItem(PCB& pcb);
void ClearFrameItem(int frame);
int Random();
int FIFO();
int LRU();
void PrintLog(QString log);
void PrintPageMap(int pid, int page, int frame);
void PrintFatalError(QString s, int pid, int page);
int GetFrameItem()
{
int ret = FP_NONE;
for(int i=0; i<FRAME_NUM; i++)
{
if( FrameTable[i].pid == FP_NONE )
{
ret = i;
break;
}
}
return ret;
}
void AccessPage(PCB& pcb)
{
int pid = pcb.getPID();
PageTable& pageTable = pcb.getPageTable();
int page = pcb.getNextPage();
if( page != FP_NONE )
{
PrintLog("Access Task" + QString::number(pid) + " for Page" + QString::number(page));
if( pageTable[page] != FP_NONE )
{
PrintLog("Find target page in page table.");
PrintPageMap(pid, page, pageTable[page]);
}
else
{
PrintLog("Target page is NOT found, need to request page ...");
pageTable[page] = RequestPage(pid, page);
if( pageTable[page] != FP_NONE )
{
PrintPageMap(pid, page, pageTable[page]);
}
else
{
PrintFatalError("Can NOT request page from disk...", pid, page);
}
}
FrameTable[pageTable[page]].ticks++;//访问页面+1
}
else
{
PrintLog("Task" + QString::number(pid) + " is finished!");
}
}
int RequestPage(int pid, int page)
{
int frame = GetFrameItem();
if( frame != FP_NONE )
{
PrintLog("Get a frame to hold page content: Frame" + QString::number(frame));
}
else
{
PrintLog("No free frame to allocate, need to swap page out.");
frame = SwapPage();
if( frame != FP_NONE )
{
PrintLog("Succeed to swap lazy page out.");
}
else
{
PrintFatalError("Failed to swap page out.", pid, FP_NONE);
}
}
PrintLog("Load content from disk to Frame" + QString::number(frame));
FrameTable[frame].pid = pid;
FrameTable[frame].pnum = page;
FrameTable[frame].ticks = 0xFF;
MoveOut.enqueue(frame);//将页框号进行插入
return frame;
}
void ClearFrameItem(int frame)
{
FrameTable[frame].pid = FP_NONE;
FrameTable[frame].pnum = FP_NONE;
for(int i=0, f=0; (i<TaskTable.count()) && !f; i++)
{
PageTable& pt = TaskTable[i]->getPageTable();
for(int j=0; j<pt.length(); j++)
{
if( pt[j] == frame )
{
pt[j] = FP_NONE;
f = 1;
break;
}
}
}
}
int Random()
{
// just random select
int obj = qrand() % FRAME_NUM;
PrintLog("Random select a frame to swap page content out: Frame" + QString::number(obj));
PrintLog("Write the selected page content back to disk.");
ClearFrameItem(obj);
return obj;
}
int FIFO()//FIFO的实现
{
// select the first page in memory to move out
int obj = MoveOut.dequeue();//出队列的操作
PrintLog("Select a frame to swap page content out: Frame" + QString::number(obj));
PrintLog("Write the selected page content back to disk.");
ClearFrameItem(obj);
return obj;
}
int LRU()
{
int obj = 0;
int ticks = FrameTable[obj].ticks;
QString s = "";
for(int i=0; i<FRAME_NUM; i++)//选择最小的页框
{
s += "Frame" + QString::number(i) + " : " + QString::number(FrameTable[i].ticks) + " ";
if( ticks > FrameTable[i].ticks )
{
ticks = FrameTable[i].ticks;
obj = i;
}
}
PrintLog(s);
PrintLog("Select the LRU frame page to swap content out: Frame" + QString::number(obj));
PrintLog("Write the selected page content back to disk.");
return obj;
}
int SwapPage()
{
return LRU();
}
void ClearFrameItem(PCB& pcb)
{
for(int i=0; i<FRAME_NUM; i++)
{
if( FrameTable[i].pid == pcb.getPID() )
{
FrameTable[i].pid = FP_NONE;
FrameTable[i].pnum = FP_NONE;
}
}
}
void PrintLog(QString log)
{
cout << log.toStdString() << endl;
}
void PrintPageMap(int pid, int page, int frame)
{
QString s = "Task" + QString::number(pid) + " : ";
s += "Page" + QString::number(page) + " ==> Frame" + QString::number(frame);
cout << s.toStdString() << endl;
}
void PrintFatalError(QString s, int pid, int page)
{
s += " Task" + QString::number(pid) + ": Page" + QString::number(page);
cout << s.toStdString() << endl;
QCoreApplication::exit(-2);
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
int index = 0;
qsrand(time(NULL));
TaskTable.append(new PCB(1));
//TaskTable.append(new PCB(2));
PrintLog("Task Page Serial:");
for(int i=0; i<TaskTable.count(); i++)
{
TaskTable[i]->printPageSerial();
}
PrintLog("==== Running ====");
while( true )
{
for(int i=0; i<FRAME_NUM; i++)//将页面计数值减一,每隔一段时间间隔触发中断
{
FrameTable[i].ticks--;
}
if( TaskTable.count() > 0 )
{
if( TaskTable[index]->running() )
{
AccessPage(*TaskTable[index]);
}
else
{
PrintLog("Task" + QString::number(TaskTable[index]->getPID()) + " is finished!");
PCB* pcb = TaskTable[index];
TaskTable.removeAt(index);
ClearFrameItem(*pcb);
delete pcb;
}
}
if( TaskTable.count() > 0 )
{
index = (index + 1) % TaskTable.count();
}
cin.get();
}
return a.exec();
}
运行结果
由实验结果可以得知,在进行页交换时,将页框访问次数最少的页框进行了移除
小结
1.在实验上,页框表,页表和任务结构是相互关联的关系
2.页框分配和页框回收时需要斩断页框表和页表的双向关联
3.任务结构是任务的内在表示,包含了私有的页表
4.FIFO和LRU页交换算法都是从概率的角度选择页面移除