Project 3' Virtual Memory

1
Project 3. Virtual Memory
2
Virtual Memory

• To address the limitation of physical memory size
• To provide isolation between processes
• Current pintos system
• Incomplete page table management
• Page fault causes system corruption

3
Important!

• Must Read a following PDF document carefully.
• http//www.scs.stanford.edu/07au-cs140/pintos/pint
  os.pdf
• Chapter 4.
• Appendix A.
• A.5 Memory Allocation
• A.6 Virtual Addresses
• A.7 Page Table
• A.8 Hash Table

4
Terminology

• Page
• A continuous region of virtual memory 4KB
• Frame
• A continuous region of physical memory 4KB
• Page Table (page directory)
• A data structure that the CPU uses to translate a
  virtual address to a physical address. (from a
  page to a frame)
• Pintos provides abstract interfaces to page table
  in pagedir.c
• (uint32_t )pagedir in struct thread
• Swap Slot
• A continuous page-size region of disk space on
  the swap disk

5
Overview

• Pintos

User
User Process
User Process
User Process

System calls
Kernel
Scheduler

Driver
Driver
Driver
Kernel threads

Console
Disk
6
Overview

• Pintos Project 1. Threads

User
User Process
User Process
User Process

System calls
Kernel
Scheduler

Driver
Driver
Driver
Kernel threads

Console
Disk
7
Overview

• Pintos Project 2. User Programs

User
User Process
User Process
User Process

System calls
Kernel
Scheduler

Driver
Driver
Driver
Kernel threads

Console
Disk
8
Review - Project 2. User Programs

• exec(a.out)
• Start a new kernel thread running a.out
• process_execute() ? thread_create()
• Load a.out into the thread and start it running
  (a user process)
• execute_thread

Frame table
idx
Flags
Kernel space
stack
a.out - ELF
header
User space
vaddr idx
paddr

loading


Codes Data
data

Page directory (page table)
Codes

Physical address (frames)
Virtual address (pages)
9
Tasks

• Project 3.Virtual Memory
• Swapping, Handling page faults, lazy loading

!
Frame table
idx
Flags
Kernel space
stack
a.out - ELF
header
!
vaddr idx
paddr

Lazy loading


Codes Data
data

Page directory (page table)
!
Codes

Physical address (frames)
Swapping
Virtual address (pages)
!
Swap table
Supplement page table
idx
Flags
vaddr idx
Flags
!
Swap disk
10
Tasks

• Paging - Swap, Lazy loading
• frame table allocator
• Page table management
• Supplement page table
• Swap management
• Stack growth, Memory mapped files

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Frame table allocator

• Current pintos system
• Threads/palloc.c
• Functions to allocate pages
• palloc_get_page, palloc_get_multiple
• Functions to free pages
• palloc_free_page, palloc_free_multiple
• Appendix A.5.1
• User pool/Kernel pool
• It is possible to modify palloc.c
• only parts related to user pool
• Synchronization (parallelism)
• Eviction algorithm
• LRU

Frame table
idx
Flags

Physical address (frames)
12
Page table management

• Mapping a virtual address to a physical address
• When Swap, lazy loading, page fault occur,
• To get a page_table of each threads
• uint32_t pagedir in struct thread
• Map/Unmap function
• pagedir_set_page (uint32 t pd, void upage, void
  kpage, bool writable)
• pagedir_clear_page (uint32 t pd, void upage)
• Some functions to check accessed and dirty bits
  of pages.
• pagedir_is_dirty (uint32 t pd, const void page)
• pagedir_is_accessed (uint32 t pd, const void
  page)
• pagedir_set_dirty (uint32 t pd, const void
  page, bool value)
• pagedir_set_accessed (uint32 t pd, const void
  page, bool value)
• Appendix A.7.2, A.7.3

vaddr idx
paddr


Page directory (page table)
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Supplement page table

• When page faults occur,
• To locate the page faulted.
• Lazy loading, a swap slot, an all-zero page.
• Hash table

Kernel space
stack
data

Codes

Virtual address (pages)
Supplement page table
vaddr idx
Flags
14
Swap management
Swap table

• When eviction occurs,
• swap pages evicted to swap disk.
• Interface hd11 (interface in devices/disk.h)
• struct disk disk_get(int chan_no, int dev_no)
• disk_sector_t disk_size (struct disk )
• void disk_read(struct disk, disk_sector_t,
  void)
• void disk_write(struct disk, disk_sector_t,
  void)
• Pintos --swap-diskn
• Swap disk management
• Slots information (occupied or not)
• bitmap

idx
Flags
Swap disk
15
Submission

• Due date
• 12/21 (?) ??
• Submission
• yjlee AT camars.kaist.ac.kr
• Archive of pintos/src directory
• Design documents
• TA
• ??? (x5578) ??? 4417?

16
Reference

• http//www.scs.stanford.edu/07au-cs140/pintos/pint
  os.pdf
• Chapter 4. Project 3 Virtual Memory
• Appendix A
• A.5 Memory Allocation
• A.6 Virtual Address
• A.7 Page Table
• A.8 Hash Table