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
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