21. Beyond physical memory: Mechanisms Flashcards
How is act of accessing page that is not currently in memory, but on disk, called?
Page fault
What happens on a page fault?
‘trap’ occurs, and the request is dispatched to page-fault handler which is run by OS
Why is page fault services by OS in the hardware-managed TLBs?
Because the disk access is so slow, the overhead of OS is unnoticable and hardware would also need to know how to operate with I/O directly.
Where is disk address stored when page is swapped to disk?
In bits used for PFN in PTE
What bit is used to indicate the page is not in memory right now?
Present bit
What does OS implement to decide when to evict page?
High and low watermarks.
How is LW and HW utilized?
When lower than LW pages available, a thread runs to evict all pages until HW pages available
How is thread that uses LW and HW called?
Swap or page daemon
Beside the swap space, where can some specific area of address space be swapped? And what area is it?
The code area. It can be swapped back to the file on disk where it was loaded from.
When memory is full and we need to put a page in there from swap space, how is process of choosing a current page to evict called?
Page replacement policy
How can a process that swap daemon performs be optimized?
By grouping or clustering the number of pages to write them to disk
What does OS do where is no memory to swap pages in?
It notifies swap/page daemon and it runs in background freeing up pages according to LW and HW.
