MIT6.S081笔记：lecture 4

MIT6.S081笔记：lecture 4 Page Tables

Isolation

• why use virtual memory?

• make bad code doesn’t affect the os
• want sth really seperates these memories from different programs

How to give isolation?

Address Spaces

• give applications including the kernel its own address space

• How to multiplex all these different address spaces on a single physical memory?

  PAGE TABLES (HW: memory management unit)

Blueprint

• every app has its own map which basically defines its address space

PAGE TABLE

• not per address, per page! each page is 4kB

• in xv6, virtual memory is less than physical memory space
• and it’s inefficient to store all entries(2^27)

RISC-V PAGE TABLE

• Use cache(TLB) to avoid 3 times of memory translations
• When switching page table, also need to flush the TLB

Kernel memory address space layout

• every process has a corresponding kernel stack