14-513: CSAPP 017: Virtual Memor

MMU - same chip on the processor - not the ALU - algorithmic logic unit

isolate: processes are separated!

dense mapping: waste too much PM
~> just map the used VM to PM

VM ~> can be mapped to both PM and disk

• VP and PP need to have the same size
• Phys address space can be larger or smaller than the virtual address space

VPN: virtual page number
PPN/PFN/FN: phys page number/ phys frame number/ frame number

we only look at the Virtual Page Number in the page table, rather than the virtual address

Page fault: read from disk -> slow! -> do other processes to keep CPU busy -> wait for the interrupt

operating system asking:

• bad pointer?
• OS's fault, didn't fetch the data from disk? -> OS loads data from disk

old name -> swap -> linux's (page) swap space is designed for the pages that miss

work set size main memory size -> good
work set size main memory size -> constantly communicate with disk -> bad

read-only lib -> eg. libc

virtual page and phys page use the same offset! ->great!

hollow spaces are not mapped (no entry in the system), so spaces are saved!
drawback is the calculating time is much larger (high latency) -> could be painful!
-> however, space locality again

类似于：tree search, rather than an array or a hash table???

Problem here:
the page table mapping exists in memory, probably in virtual address space, how do we translate it???

it stores the mapping from virtual memory to phys memory