CS533 Concepts of Operating Systems Class 14 Extensible Virtual Memory Management

CS533 - Concepts of Operating Systems 2 Questions  What is an inverted page table? o Why are they good for large sparse address spaces?  How are address maps, memory allocation queues, memory object lists, memory objects, resident page tables, and pmap used to o Handle a page fault? o Page out a page? o Allocate memory o Deallocate memory

CS533 - Concepts of Operating Systems 3 Questions  Why does Mach distinguish between current and maximum protection for pages?  Why are shadow objects needed? o How would task A share a page copy-on-write with task B? o Why might you end up with long chains of shadow objects? o Why is this a problem? o How could you optimize them?

CS533 - Concepts of Operating Systems 4 Questions  How can Mach support lazy modification of pmap?  Why don’t inverted page tables support aliasing well?  What three strategies can Mach use to maintain TLB consistency on multiprocessors that do not support inter-CPU TLB flush operations? o Which one reminds you of RCU and why?

CS533 - Concepts of Operating Systems 5 Questions  Why push virtual memory fault handling to user level? o What kind of user-level instructions can it replace? o Is it always more efficient to use VM faults than user-level interpretation? o What are the performance trade-offs?  Can VM fault handling be used to implement synchronization? o i.e., instead of locks? If so, how?

CS533 - Concepts of Operating Systems 6 Questions  Why are these technique more difficult to use on modern CPUs with deep pipelines, out of order instructions and weak memory consistency?  Why do hardware details such as physically vs virtually indexed caches affect aliasing costs?  Why do OS details such as inverted page tables affect aliasing costs?