Đang tải... (xem toàn văn)
Tiểu luận môn Giải thuật nâng cao chủ đề Virtual Memory Run multiple processes, each with its own address space main memory can’t contain all. Many processes use only a small part of space Small parts : main memory Other parts : disk Virtual memory : technique of sharing main memory among many processes. Main mem ~ cache for the disk
LOGO Virtual Memory Nhóm 5 11070459 - Thái Tiểu Minh 11070460 - Nguyễn Kim Ngân 13070249 - Lê Minh Nam 13070250 - Trần Đức Nghĩa 13070251 - Phạm Ích Trí Nhân 13070247 - Trần Thị Mi 1 Contents A Introduction B Replacement C Segmentation D Protection E Examples 2 A Introduction Reasons for using virtual memory Share main memory Simplify memory management Provide protection What is a virtual memory? Memory Hierarchy Virtual memory vs Cache 3 1 Reason 1 Run multiple processes, each with its own address space main memory can’t contain all Many processes use only a small part of space Small parts : main memory Other parts : disk Virtual memory : technique of sharing main memory among many processes Main mem ~ cache for the disk 4 1 Reason 2 A program is too large for main mem programmers have to make it fit (*) Program is devided into pieces mem/disk Only “active” code, data : main mem Virtual memory : Relieves progammer’s job Automatically manages memory accesses between main memory and disk (secondary storage) Simplify memory management 5 1 Reason 3 Virtual memory : One process can’t interfere with another • Because they operate in different address spaces User process cannot access privileged information • Different sections of address spaces have different permissions Provide protection 6 2 Memory Hierarchy Cache CPU CPU regs regs 8B Virtual memory 32 B Cache Register Cache 4 KB Memory Memory Memory Disk Disk Disk Memory size: 32 B 32 KB-4MB 4096 MB 1 TB speed: 0.3 ns 2 ns? 7.5 ns 8 ms $75/MB $0.014/MB $0.00012/MB 32 B 4 KB $/Mbyte: line size: 4B larger, slower, cheaper 7 2 Virtual Memory 8 2 Virtual Memory Virtual memory = memory on disk Virtual memory : logical address (virtual address) Main mem : physical address Contains blocks from main mem and disk Controlled by operation system Auto overlay (+) Virtual continuous address space (+) Size ~ disk size, speed ~ main mem speed (+) Programmers don’t care about mem size run more larger processes 9 3 Virtual Memory vs Cache 10 Address Translation Addressing 8 14-bit virtual addresses (virtual mem size = 2 ) 6 12-bit physical addresses (phy mem size = 2 ) 6 Page size = 64 bytes = 2 Offset = 6bit (Virtual Page Offset) (Virtual Page Number) V# 13 12 11 10 VO 9 8 7 P# (Physical Page Number) 51 6 5 4 3 2 1 PO (Physical Page Offset) 0 TLB (Translation Look-aside Buffer) 4-way Associative TLB 2 TLBIndex = 2bit (do 2 set) 8 2 TLBTag = lg(virtual size/sets) = lg(2 / 2 ) = 6bit TLBTag 13 12 11 10 I 9 8 7 6 5 4 3 V# 2 1 0 VO Set Tag P# Valid Tag P# Valid Tag P# Valid Tag P# Valid 0 03 – 0 09 0D 1 00 – 0 07 02 1 1 03 2D 1 02 – 0 04 – 0 0A – 0 2 02 – 0 08 – 0 06 – 0 03 – 0 3 07 – 0 03 0D 1 0A 34 1 02 – 0 52 Page Table Only show first 16 entries (max 28 = 64 entries) VPN : 0000.1000 08; … PPN : 10.1000 28; 11.0011 33 V# (8) P# (6) Valid(1) V# P# Valid 00 28 1 08 13 1 01 – 0 09 17 1 02 33 1 0A 09 1 03 02 1 0B – 0 04 – 0 0C – 0 05 16 1 0D 2D 1 06 – 0 0E 11 1 07 – 0 0F 0D 1 53 Cache Cache 16 lines, 4-byte line size, Direct mapped CTag 11 10 9 CIndex 8 7 6 5 4 CO 3 P# 2 1 0 PO Idx Tag Valid B0 B1 B2 B3 Idx Tag Valid B0 B1 B2 B3 0 19 1 99 11 23 11 8 24 1 3A 00 51 89 1 15 0 – – – – 9 2D 0 – – – – 2 1B 1 00 02 04 08 A 2D 1 93 15 DA 3B 3 36 0 – – – – B 0B 0 – – – – 4 32 1 43 6D 8F 09 C 12 0 – – – – 5 0D 1 36 72 F0 1D D 16 1 04 96 34 15 6 31 0 – – – – E 13 1 83 77 1B D3 7 16 1 11 C2 DF 03 F 14 0 – – – – 54 Example 1 – TLB hit & Page hit Virtual Address 0x03D4 4 D 3 0 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 1 1 1 1 0 1 0 1 0 0 0 1 F 8 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 1 1 1 1 0 1 0 1 0 0 V#=0F VO=18 TLBT=03 0 TLBI=3 3 3 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 1 1 1 1 0 1 0 1 0 0 Example 1 – TLB hit & Page hit TLBT=03 Virtual Address 0x03D4 TLBI=3 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 1 1 1 1 0 1 0 1 0 0 Looking in TLB : TLB Index check TLB Tag check Valid bit TLB Index = 3 Tag 03 exists & Valid = 1 TLB hit ( Page hit) P# = 0D Set Tag P# Valid Tag P# Valid Tag P# Valid Tag P# Valid 3 07 – 0 03 0D 1 0A 34 1 02 – 0 56 Example 1 – TLB hit & Page hit Virtual Address 0x03D4 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 1 1 1 1 0 1 0 1 0 0 VO=18 Physical Address D 0 11 10 9 8 7 6 5 4 3 2 1 0 0 0 1 1 0 1 0 1 0 1 0 0 P#=0D PO=18 CT=0D CI=5 0 D CO=0 5 0 11 10 9 8 7 6 5 4 3 2 1 0 0 0 1 1 0 1 0 1 0 1 0 0 57 Example 1 – TLB hit & Page hit Physical Address CT=0D CI=5 CO=0 11 10 9 8 7 6 5 4 3 2 1 0 0 0 1 1 0 1 0 1 0 1 0 0 Looking in Cache Cache Index check Cache Tag check valid bit Index = 5 Tag 0D exists & valid = 1 Cache hit Offset = 0 take B0 : byte 36 Idx Tag Valid B0 B1 B2 B3 5 0D 1 36 72 F0 1D 58 Example 1 – TLB hit & Page hit TLBT=03 Virtual Address 0x03D4 TLBI=3 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 1 1 1 1 0 1 0 1 0 0 V#=0F VO=18 CPU TLB : TLB Hit (Index,Tag), Page Hit P# = 0D Physical Address CT=0D CI=5 CO=0 11 10 9 8 7 6 5 4 3 2 1 0 0 0 1 1 0 1 0 1 0 1 0 0 P#=0D Cache : Cache Hit Byte : 36 59 PO=18 Example 1 - TLB hit & Cache hit data data virtual physical addr addr hit Processor hit TLB miss Cache Main Memory miss Page hit Page OS Fault Table Handler page fault/ protection violation 60 Disk Memory Example 2 – TLB miss & Page hit data data virtual physical addr addr hit Processor hit TLB miss Cache Main Memory miss Page hit Page OS Fault Table Handler page fault/ protection violation 61 Disk Memory Example 2 – TLB miss & Page hit TLBT=02 Virtual Address 0x028F TLBI=2 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 1 0 1 0 0 0 1 1 1 1 V#=0A VO=0F TLB : TLB Miss (Index,Tag), Page Hit(V#) P# = 09 Physical Address CT=09 CI=3 CO=3 11 10 9 8 7 6 5 4 3 2 1 0 0 0 1 0 0 1 0 0 1 1 1 1 P#=09 Cache : Cache Miss Byte : ?? (main mem) 62 PO=0F Example 3 – TLB miss & Page fault data data virtual physical addr addr hit Processor hit TLB miss Cache Main Memory miss Page hit Page OS Fault Table Handler page fault/ protection violation 63 Disk Memory Example 3 – TLB miss & Page fault TLBT=00 Virtual Address 0x0040 TLBI=1 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 V#=01 VO=00 TLB : TLB Miss (Index,Tag), Page Fault(V#) P#=… Physical Address CT 11 10 9 CI 8 7 P# Byte : ?? (disk or nonexistent) 64 6 5 4 CO 3 2 PO 1 0 LOGO Thank You ! 65 ... $/Mbyte: line size: 4B larger, slower, cheaper Virtual Memory Virtual Memory Virtual memory = memory on disk Virtual memory : logical address (virtual address) Main mem : physical address... Introduction Reasons for using virtual memory Share main memory Simplify memory management Provide protection What is a virtual memory? Memory Hierarchy Virtual memory vs Cache Reason ... permissions Provide protection Memory Hierarchy Cache CPU CPU regs regs 8B Virtual memory 32 B Cache Register Cache KB Memory Memory Memory Disk Disk Disk Memory size: 32 B 32 KB-4MB 4096 MB