21 - Swapping Mechanisms

Memory hierarchy

mechanisms require an additional level in the _ _

Hard Disk Drive

in modern systems, this role is usually served by a _ _ _

Register, Cache, Main Memory, Mass Storage

memory hierarchy in modern systems (top to down)

Manually manage

easier for programmers – no need to _ _ the memory used by a process

Swap Space, Multiple Concurrently Running Process

_ _ allows the OS to support the illusion of a large virtual memory for _ _ _ _ since early systems don’t have enough main memory

Swap Space

reserve some space on the disk for moving pages back and forth

Page Sized Unit

OS need to remember to the swap space in _ _ _

Present Bit

add some machinery higher up in the system in order to support swapping pages to and from the disk

Present, Physical

when the hardware looks in the PTE, it may find that the page is not _ in _ memory

Present

meaning of 1, page is _ in physical memory

Disk

meaning of 0, the page is not in memory but rather on _

Page Replacement Policy

the process of picking a page to kick out or replace

Page Fault

accessing page that is not in physical memory

Memory

if a page is not present and has been swapped out to disk, the OS need to swap the page into _ in order to service the page fault

PTE

is used for data such as the PFN of the page for a disk address

Soon be faulted in page

the OS must find a physical frame for the _ _ _ _ _ to reside within, page fault control flow – software

Replacement Algorithm

if there is no such page, waiting for the _ _ to run and kick some pages out of memory, page fault control flow - software

Full, Make room

OS waits until memory is entirely _ and only then replaces a page to _ _ for some other page

Low Watermark Page

there are fewer than _ _ _available, a background thread that is responsible for freeing memory runs, swap Daemon, page Daemon

High Watermark pages

the thread evicts pages until there are _ _ _ available, swap Daemon, page Daemon