paging scheme

Concept

• logical space is contiguous
• physical space can be disjoint
• have a lookup table to map between the two

memory context is essentially this page table, not the full memory space used by the process

Page sharing

Data sharing

• what shared memory can do
• logical pages from two processes can be mapped to the same physical frame

Copy-on-write

• fork doesn’t duplicate all the process memory, it uses page sharing, since both processes are identical
• only when there is a write, then the frame is copied to differentiate the two processes

Translation Look-aside Buffer(TLB)

• cache of a few page table entries
• TLB-hit:
  • frame number is retrieved to generate physical address
• TLB-miss:
  • access full page table in memory
  • retrieve frame number to generate physical address and update TLB
• TLB has to be flushed during context switching

Access-right bits

• access control probabily links to this

Valid bit

• indicates whether the page is valid to access
• visiting an unused/out-of-range page will trigger an exception

segmentation fault