主存作为虚存的Cache:换入换 Virtual address space Physical address space 0x00000000 0x00010000 swap out 0□1☐2☐3☐ text 0x00000000 456古7己 program A 8☐9☐10☐11☐ 0x10000000 12☐13☐14☐15☐ data swap in 16☐171819 program 20☐21☐22☐23■ B 磁盘交换区(swap space) MainMemory 换入/换出时机？ Ox00ffffff Demand Paging策略 stack Bring a page into memory page belonging to process only when it is needed Ox 71fff page not belonging to process 1.Less 1/O needed 2.Less memory needed 3.Faster response 4.More users主存作为虚存的Cache：换入换出 磁盘交换区（swap space） 换入/换出时机？ Demand Paging策略 Bring a page into memory only when it is needed 1. Less I/O needed 2. Less memory needed 3. Faster response 4. More users