20. Paging: Smaller Tables

Question 1

Why is larger page tables not a good idea?

Answer 1

Although we are able to have lesser number of page tables, there will be internal fragmentation

Question 2

What is internal fragmentation?

Answer 2

A situation when there is unused space in a page

Question 3

Why is the hybrid approach of using segmentation and page tables bad?

Answer 3

There will still be internal and external fragmentation.

Question 4

What is a page directory?

Answer 4

A data structure that is used in multi-level paging to map the addresses of page tables

Question 5

What is multi-level paging?

Answer 5

A memory management technique that uses a hierarchy of page tables to map virtual addresses to physical addresses.

Question 6

What is a page directory entry (PDE)?

Answer 6

Similar to a PTE, it has a valid bit and a PFN.

Question 7

What are the advantages of multi-level page tables?

Answer 7

1. Compact and supports sparse address spaces
2. The page tables do not need to be in a contiguous block of memory

Question 8

What are the disadvantages of multi-level page tables?

Answer 8

1. Complexity
2. Increased memory accesses when TLB misses

Question 9

What is an inverted page table?

Answer 9

A memory management technique where there is a single page table that has an entry for each physical page. Each entry will have the mapping from virtual to physical and which process is currently using it