nachos 内存管理和多进程实现

来源：互联网发布：我是山姆知乎编辑：程序博客网时间：2024/04/29 17:04

1.首先利用位图来管理内存
mBitmap = new BitMap(NumPhysPages);

2.创建用户空间时，首先从位图中找到一个空闲页，如果没有空间为，置为0，并标识valid = FALSE

 pageTable = new TranslationEntry[numPages];    for (i = 0; i < numPages; i++) {pageTable[i].virtualPage = i;// for now, virtual page # = phys page #int ppn = machine->mBitmap->Find();//查找一个空闲块if(ppn != -1) //如果有空闲块{pageTable[i].physicalPage = ppn;pageTable[i].valid = TRUE;}else //如果没有空闲块，无法将该页放入内存{pageTable[i].physicalPage = 0;pageTable[i].valid = FALSE;}pageTable[i].use = FALSE;pageTable[i].dirty = FALSE;pageTable[i].readOnly = FALSE;  // if the code segment was entirely on // a separate page, we could set its // pages to be read-only    }

3.修改读入内存的代码，每次只读一个字节

   if (noffH.code.size > 0) {        DEBUG('a', "Initializing code segment, at 0x%x, size %d\n", noffH.code.virtualAddr, noffH.code.size);for(int i = 0;i<noffH.code.size;i++){vAddr = noffH.code.virtualAddr + i;vpn = vAddr/PageSize;//虚拟页号offset = vAddr%PageSize;//偏移量if(pageTable[vpn].valid != FALSE){ ppn = pageTable[vpn].physicalPage;      //物理块号pAddr = ppn*PageSize + offset;      //物理地址executable->ReadAt(&(machine->mainMemeory[pAddr],1,noffH.code.inFileAddr+i));}}    }    if (noffH.initData.size > 0) {for(int i = 0;i<noffH.initData.size;i++){vAddr = noffH.initData.virtualAddr + i;vpn = vAddr/PageSize;//虚拟页号offset = vAddr%PageSize;//偏移量if(pageTable[vpn].valid != FALSE){ ppn = pageTable[vpn].physicalPage;//物理块号pAddr = ppn*PageSize + offset;//物理地址executable->ReadAt(&(machine->mainMemeory[pAddr],1,noffH.initData.inFileAddr+i));}}    }