Virtual Memory Part 1

Question 1

Instructions must be in ________ memory to be executed

Answer 1

physical

Question 2

What is program size limited to?

Answer 2

Physical memory size

Question 3

Physical memory cannot support a lot of processes. Thus ________ suffers

Answer 3

multiprogramming

Question 4

We desire to allow some portions of the address space to be ___-_______ _________

Answer 4

non-memory resident

Question 5

Non-memory resident means not in ______ memory

Answer 5

physical

Question 6

What is demand paging?

Answer 6

Loading program code/data pages into memory on demand

Question 7

An item that could be a candidate for demand paging are _____ _______

Answer 7

shared libraries

Question 8

Swapping is when the OS stashes ______ pages away to the _____ ______ backed by stable storage

Answer 8

memory, swap space

Question 9

Virtual memory gives the application the illusion of an ________ amount of memory

Answer 9

infinite

Question 10

_______ memory supports more processes concurrently

Answer 10

virtual

Question 11

What are 2 related approaches to virtual memory?

Answer 11

Swapping and demand paging

Question 12

In demand paging, a page is brought into memory only when ______

Answer 12

needed

Question 13

What are 3 benefits of demand paging?

Answer 13

• Less I/O need
• Faster response (We only load needed pages)
• More processes admitted to the system

Question 14

In demand paging, a process generates ______ (_____) addresses which are mapped to physical addresses using a ____ ____

Answer 14

logical, virtual, page table

Question 15

In demand paging, if a requested ____ is not in memory, the _____ brings it from the hard disk

Answer 15

page, kernel

Question 16

What is the swap space?

Answer 16

Storage space reserved for moving pages back and forth between storage and memory

Question 17

With swap spacing, physical memory is represented in ______ and swap space is represented in ______

Answer 17

pages, blocks

Question 18

In swap spacing, ____ size equals ____ size

Answer 18

page, block

Question 19

In traditional swap spacing, _______ processes are swapped out (meaning all of its _____)

Answer 19

entire, pages

Question 20

In modern implementation of swap spacing, only _____ of processes are swapped out

Answer 20

portions

Question 21

How do we know if a page is in memory?

Answer 21

Each page table entry has a valid/present bit

Question 22

A valid/present bit of 1 means the page is _________

Answer 22

in-memory

Question 23

A valid/present bit of 0 means the page is _________

Answer 23

not-in-memory

Question 24

During an address translation, if the valid bit equals 0, what to outcomes are there?

Answer 24

• Illegal reference (outside address space)

- Legal reference but not in memory

Question 25

If there was an illegal reference during address translation, the OS must ____ the process

Answer 25

abort

Question 26

A page fault is when the OS sets up a ____ page table entry

Answer 26

valid

Question 27

What are the 6 steps in handling a page fault?

Answer 27

``` 1. OS figures out: •Invalid reference ➔abort process •Just not in memory ➔bring page in 2. Locate page on disk 3. Find a free page frame 4. Swap page from disk to frame (I/O operation) 5. Reset page table, set valid bit to 1 6. Restart the instruction that caused page fault ```

Question 28

Virtual memory allows faster/efficient process creation using ________________

Answer 28

copy-on-write (COW)

Question 29

What does copy-on-write allow?

Answer 29

COW allows both parent and child processes to initially share the same pages in memory (during fork())

Question 30

During COW, if either _______ or _____ process modifies a shared page, the page is ______-

Answer 30

parent, child, copied

Question 31

A Major Page fault means the page needs to be brought from ____

Answer 31

disk

Question 32

A major Page fault is __________ and includes ___

Answer 32

expensive, I/O

Question 33

A Minor Page fault not need to bring a page from ______

Answer 33

disk

Question 34

A Minor Page fault is typically very _______ and just _______ the page table

Answer 34

fast, updates

Question 35

Shared pages already in memory that are ____ _________ with the process address space is an example of a _____ page fault

Answer 35

not linked, minor

Question 36

Malloc-ing where the ______ may not actually allocate physical memory until it is ________ is an example of a ______ page fault. This can become a ________

Answer 36

kernel, accessed, minor, bottleneck

Question 37

What does the command "ps -eomin_flt,maj_flt,pid,cmd" do?

Answer 37

Prints minor and major page faults for all (-e) processes running in the system with the format (-o) specified

Question 38

Which linux command reports information about processes, memory paging, IO, traps, etc?

Answer 38

vmstat

Question 39

Which linux command displays page size?

Answer 39

getconf PAGESIZE

Question 40

What does the command "sync; /bin/echo 3 > /proc/sys/vm/drop_caches;" do?

Answer 40

Clears OS caches, but it needs sudo or root privileges