Virtual Memory 1 Changelog Changes made in this version not seen - PowerPoint PPT Presentation

Virtual Memory 1

Changelog Changes made in this version not seen in fjrst lecture: 16 November 2017: shared libraries: clarifjed that it’s multiple read-only virtual copies backed by one physical copy 1

SIMD notes (1) sorry for two typos: partial_sums = _mm_setzero_si128() , not (crazy markdown formatting error) …and _mm_mullo_epi32 truncated to 32-bits (not 16) lab solutions posted on Collab, resources tab useful for HW? 2

SIMD notes (2) don’t try to use array indexing on __m128i variables compiler doesn’t know what size values you put in it _mm_extract_epi16(some_vector, 3) reads 3rd 16-bit integer in some_vector or store/load from array on the stack 3

SIMD notes (2) _mm_setr_epi16(a[i], a[i+1], a[i+2], ...) is much slower than _mm_loadu_si128((__m128i*) &a[i]) (GCC doesn’t fjgure out that a[i] and a[i+1] are adjacent… so it makes a temporary array on the stack, element-by-element) but _mm_setr_epi16 , etc. are good for constants 4

program memory 0xFFFF FFFF FFFF FFFF 0xFFFF 8000 0000 0000 0x7F… 0x0000 0000 0040 0000 Used by OS Stack Heap / other dynamic Writable data Code + Constants 5

Recall: address space Program B code = kernel-mode only trigger error real memory … OS data Program B data Program A data Program A code illuision of dedicated memory (set by OS) mapping (set by OS) mapping addresses Program B addresses Program A 6

can be difgerent sizes! address translation Program A data real addresses are ‘physical’ program addresses are ‘virtual’ “physical” real memory … OS data Program B data Program B code Program A Program A code format? stored in processor? (set by OS) mapping instructions and data every address accessed “virtual” addresses 7

can be difgerent sizes! address translation Program A data real addresses are ‘physical’ program addresses are ‘virtual’ “physical” real memory … OS data Program B data Program B code Program A Program A code format? stored in processor? (set by OS) mapping instructions and data every address accessed “virtual” addresses 7

address translation Program A data can be difgerent sizes! real addresses are ‘physical’ program addresses are ‘virtual’ “physical” real memory … OS data Program B data Program B code Program A Program A code format? stored in processor? (set by OS) mapping instructions and data every address accessed “virtual” addresses 7

can be difgerent sizes! address translation Program A data real addresses are ‘physical’ program addresses are ‘virtual’ “physical” real memory … OS data Program B data Program B code Program A Program A code format? stored in processor? (set by OS) mapping instructions and data every address accessed “virtual” addresses 7

on virtual address sizes virtual address size = size of pointer? often, but — sometimes part of pointer not used example: typical x86-64 only use 48 bits rest of bits have fjxed value virtual address size is amount used for mapping 8

address space sizes amount of stufg that can be addressed = address space size based on number of unique addresses what if my machine has 3GB of memory (not power of two)? not all addresses in physical address space are useful most common situation (since CPUs support having a lot of memory) 9 e.g. 32-bit virtual address = 2 32 byte virtual address space e.g. 20-bit physical addresss = 2 20 byte physical address space

address space sizes amount of stufg that can be addressed = address space size based on number of unique addresses what if my machine has 3GB of memory (not power of two)? not all addresses in physical address space are useful most common situation (since CPUs support having a lot of memory) 9 e.g. 32-bit virtual address = 2 32 byte virtual address space e.g. 20-bit physical addresss = 2 20 byte physical address space

toy program memory virtual page# 1 rest of address is called page ofgset (because page size is power of two) page number is upper bits of address “virtual” = addresses the program sees bytes in this case) divide memory into pages ( virtual page# 3 virtual page# 2 virtual page# 0 code 11 1111 1111 = 0x3FF 11 0000 0000 = 0x300 10 0000 0000 = 0x200 01 0000 0000 = 0x100 00 0000 0000 = 0x000 stack empty/more heap? data/heap 10

toy program memory virtual page# 1 rest of address is called page ofgset (because page size is power of two) page number is upper bits of address “virtual” = addresses the program sees bytes in this case) divide memory into pages ( virtual page# 3 virtual page# 2 virtual page# 0 code 11 1111 1111 = 0x3FF 11 0000 0000 = 0x300 10 0000 0000 = 0x200 01 0000 0000 = 0x100 00 0000 0000 = 0x000 stack empty/more heap? data/heap 10

toy program memory code rest of address is called page ofgset (because page size is power of two) page number is upper bits of address “virtual” = addresses the program sees virtual page# 3 virtual page# 2 virtual page# 1 virtual page# 0 11 1111 1111 = 0x3FF 11 0000 0000 = 0x300 10 0000 0000 = 0x200 01 0000 0000 = 0x100 00 0000 0000 = 0x000 stack empty/more heap? data/heap 10 divide memory into pages ( 2 8 bytes in this case)

toy program memory virtual page# 1 rest of address is called page ofgset (because page size is power of two) page number is upper bits of address “virtual” = addresses the program sees bytes in this case) divide memory into pages ( virtual page# 3 virtual page# 2 virtual page# 0 code 11 1111 1111 = 0x3FF 11 0000 0000 = 0x300 10 0000 0000 = 0x200 01 0000 0000 = 0x100 00 0000 0000 = 0x000 stack empty/more heap? data/heap 10

toy program memory virtual page# 1 rest of address is called page ofgset (because page size is power of two) page number is upper bits of address “virtual” = addresses the program sees bytes in this case) divide memory into pages ( virtual page# 3 virtual page# 2 virtual page# 0 code 11 1111 1111 = 0x3FF 11 0000 0000 = 0x300 10 0000 0000 = 0x200 01 0000 0000 = 0x100 00 0000 0000 = 0x000 stack empty/more heap? data/heap 10

toy physical memory 010 (2) physical page 7 virtual page # physical page # 00 01 physical page 0 111 (7) 10 none 11 000 (0) page table! physical page 1 111 1111 1111 program memory 10 1111 1111 virtual addresses 00 0000 0000 to 00 1111 1111 01 0000 0000 to 01 1111 1111 10 0000 0000 to 11 0000 0000 to 111 0000 0000 to 11 1111 1111 real memory physical addresses 000 0000 0000 to 000 1111 1111 001 0000 0000 to 001 1111 1111 11

toy physical memory 010 (2) physical page 7 virtual page # physical page # 00 01 physical page 0 111 (7) 10 none 11 000 (0) page table! physical page 1 111 1111 1111 program memory 10 1111 1111 virtual addresses 00 0000 0000 to 00 1111 1111 01 0000 0000 to 01 1111 1111 10 0000 0000 to 11 0000 0000 to 111 0000 0000 to 11 1111 1111 real memory physical addresses 000 0000 0000 to 000 1111 1111 001 0000 0000 to 001 1111 1111 11

toy physical memory 010 (2) physical page 7 virtual page # physical page # 00 01 physical page 0 111 (7) 10 none 11 000 (0) page table! physical page 1 111 1111 1111 program memory 10 1111 1111 virtual addresses 00 0000 0000 to 00 1111 1111 01 0000 0000 to 01 1111 1111 10 0000 0000 to 11 0000 0000 to 111 0000 0000 to 11 1111 1111 real memory physical addresses 000 0000 0000 to 000 1111 1111 001 0000 0000 to 001 1111 1111 11

toy physical memory 010 (2) physical page 7 virtual page # physical page # 00 01 physical page 0 111 (7) 10 none 11 000 (0) page table! physical page 1 111 1111 1111 program memory 10 1111 1111 virtual addresses 00 0000 0000 to 00 1111 1111 01 0000 0000 to 01 1111 1111 10 0000 0000 to 11 0000 0000 to 111 0000 0000 to 11 1111 1111 real memory physical addresses 000 0000 0000 to 000 1111 1111 001 0000 0000 to 001 1111 1111 11

toy physical memory 010 (2) physical page 7 virtual page # physical page # 00 01 physical page 0 111 (7) 10 none 11 000 (0) page table! physical page 1 111 1111 1111 program memory 10 1111 1111 virtual addresses 00 0000 0000 to 00 1111 1111 01 0000 0000 to 01 1111 1111 10 0000 0000 to 11 0000 0000 to 111 0000 0000 to 11 1111 1111 real memory physical addresses 000 0000 0000 to 000 1111 1111 001 0000 0000 to 001 1111 1111 11

01 1101 0010 — address from CPU toy page table lookup 111 1101 0010 1 000 (0, stack) 1 1 trigger exception if 0? to cache (data or instruction) 0 “page table entry” “virtual page number” “physical page number” “page ofgset” “page ofgset” 11 0 virtual 1 OK? write OK? 00 1 010 (2, code) 0 ??? (ignored) 01 1 111 (7, data) 1 1 10 0 12 page # valid? physical page # read

toy page table lookup 111 1101 0010 11 1 000 (0, stack) 1 1 trigger exception if 0? to cache (data or instruction) virtual “page table entry” “virtual page number” “physical page number” “page ofgset” “page ofgset” 0 0 ??? (ignored) 1 OK? write OK? 00 1 010 (2, code) 0 0 01 1 111 (7, data) 1 1 10 12 01 1101 0010 — address from CPU page # valid? physical page # read