Table of Contents

Virtual Memory - Page (memory page|virtual page|chunk)

About

A page is the unit of data processed by paging.

In a virtual memory process, with an MMU, memory addresses go through a translation step prior to each memory access.

This means that memory address 123 might be directed to physical address 82043 at one time, and physical address 20468 another time. As it turns out, the overhead of individually tracking the virtual to physical translations for billions of bytes of memory would be too great.

Virtual Memory

Instead, the MMU divides RAM into page (known also as memory page or virtual page) which are contiguous sections of memory of a set size that are handled by the MMU as single entities.

Each pages (chunk) can have different states such as:

In Linux, those chunks are typically 4Kb.

Property

Shared

Shared page are shared between process. How many processes share is not known. See Virtual Memory - Shared Memory (SHM)

Management

Size

A memory page can be both in memory and on disk, and if you sum up everything in memory and everything on disk you will count the page twice.

Shared pages are even more complicated, as only the fact that they are shared is known. How many processes share is not known. If you sum up all the processes memory that is “in RAM” you will count the shared pages multiple times.

Swap

See Virtual Memory - Paging or Swapping

in

see page in

out

see Page Out

fault

see Memory - Page Fault Exception

Documentation / Reference