Summary of Memory Management Terms

This article was originally published on bmf-tech.com.

Overview

While reading the memory management chapter of Understanding Linux Internals, I encountered some terms that I didn't fully understand, so I picked a few and summarized them.

OOM

• Out of memory
• A state where the system cannot allocate new memory because it has exhausted both physical and virtual memory
• OOM Killer (Out of Memory Killer)
  • A mechanism in the Linux kernel that forcibly terminates processes to free up memory when OOM occurs

Virtual Memory

• Memory that the OS virtualizes to appear as main storage
• Treats scattered addresses on physical memory as sequential addresses
• A feature that considers part of the hard disk as virtual memory addresses
  • → Swap

Page Table

• A data structure used in the OS's virtual memory to map virtual addresses to physical addresses

Page Fault

• An interrupt or exception generated by hardware when a program accesses a page in the virtual address space that is not mapped to physical memory

File Map

• Mapping a file into memory
  • In C language, this can be done with mmap
  • Similar to performing paging or swapping by the OS within one's own process

Demand Paging

• A type of memory management
• A method where physical memory is allocated to a page when the memory content of the corresponding address is needed

Copy-on-Write

• A mechanism where copying is done at the time of writing
• When creating a child process from a parent process, it temporarily shares the parent's memory space (with write protection specified) without copying all data in the parent's memory, thus reducing the processing time for process creation
• When either process issues a write request to the shared memory space, a new memory space is allocated, and the data in memory is copied
• This is the method

Swap

• An OS feature that increases memory capacity by securing a storage area called a swap file or swap space on auxiliary storage devices like hard disks
• Also, in paged virtual memory, swapping or page swapping refers to exchanging pages between physical memory and auxiliary storage

References

• Wikipedia- OOM
• Nikkei XTECH - OOM Killer
• Wikipedia - Virtual Memory
• Milestone of SE - The Essence and Mechanism of Virtual Memory (Virtual Memory), Benefits ~ Swap, MMU, Paging Table ~
• Wikipedia - Page Table
• Wikipedia - Page Fault
• Computer: C Language Course: About mmap
• IT Terminology Dictionary Binary
• Wikipedia - Copy-on-Write
• Nikkei XTECH - Copy-on-Write
• IT Terminology Dictionary - Swap 【 swap 】 Memory Swap / memory swap