Special features of Linux memory management mechanism

Introduction

In this article, I am going to describe some general features and some specific ones of the memory management in Linux. It will be mainly on dynamic memory allocation and release, as well as the management of the free memory. The article concerns the Linux kernel versions 2.6.X.

Structure of the Linux memory management

The term “memory management” refers to the mechanisms implemented by an operating system to provide applications with memory-related services. These services include usage of virtual memory (utilizing of a hard disk or other non-RAM storage media to provide additional program memory), protected memory (exclusive access to a region of memory by a process), and shared memory (cooperative access to a region of memory by multiple processes).

Memory management services in the Linux are built on a programming foundation that includes a peripheral device called Memory Management Unit (MMU). MMU translates physical memory addresses to linear addresses used by the operating system, and requests a page fault interrupt, when the CPU tries to access memory that it is not entitled to.

Not all processors have MMUs. Therefore, the uClinux distribution (Linux for microcontrollers) supports a single address space of operation. This architecture lacks the protection provided by MMU but makes it possible for Linux to run on another class of processors.

For further understanding of structure of the MM services, we need to know that a basic unit of memory under Linux is page, a non-overlapping region of contiguous memory. All available physical memory is organized into pages towards the end of the kernel’s boot process. Size of page depends on processor architecture. Processor designs often allow to have two or more, sometimes simultaneously, page sizes.

Traditional page size used by Linux is 4096 bytes.

Read more: Codeproject

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