Book Image

Linux Kernel Programming

By : Kaiwan N. Billimoria
Book Image

Linux Kernel Programming

By: Kaiwan N. Billimoria

Overview of this book

Linux Kernel Programming is a comprehensive introduction for those new to Linux kernel and module development. This easy-to-follow guide will have you up and running with writing kernel code in next-to-no time. This book uses the latest 5.4 Long-Term Support (LTS) Linux kernel, which will be maintained from November 2019 through to December 2025. By working with the 5.4 LTS kernel throughout the book, you can be confident that your knowledge will continue to be valid for years to come. You’ll start the journey by learning how to build the kernel from the source. Next, you’ll write your first kernel module using the powerful Loadable Kernel Module (LKM) framework. The following chapters will cover key kernel internals topics including Linux kernel architecture, memory management, and CPU scheduling. During the course of this book, you’ll delve into the fairly complex topic of concurrency within the kernel, understand the issues it can cause, and learn how they can be addressed with various locking technologies (mutexes, spinlocks, atomic, and refcount operators). You’ll also benefit from more advanced material on cache effects, a primer on lock-free techniques within the kernel, deadlock avoidance (with lockdep), and kernel lock debugging techniques. By the end of this kernel book, you’ll have a detailed understanding of the fundamentals of writing Linux kernel module code for real-world projects and products.
Table of Contents (19 chapters)
1
Section 1: The Basics
6
Writing Your First Kernel Module - LKMs Part 2
7
Section 2: Understanding and Working with the Kernel
10
Kernel Memory Allocation for Module Authors - Part 1
11
Kernel Memory Allocation for Module Authors - Part 2
14
Section 3: Delving Deeper
17
About Packt

Understanding the OOM score

In order to speed up the discovery of what the memory-hogging process is at crunch time (when the OOM killer is invoked), the kernel assigns and maintains an OOM score on a per-process basis (you can always look up the value in the /proc/<pid>/oom_score pseudo-file).

The OOM score range is 0 to 1000:

  • An OOM score of 0 implies that the process is not using any memory available to it
  • An OOM score of 1000 implies the process is using 100 percent of the memory available to it

Obviously, the process with the highest OOM score wins. Its reward – it is instantly killed by the OOM killer (talk about dry humor). Not so fast though: the kernel has heuristics to protect important tasks. For example, the baked-in heuristics imply that the OOM killer will not select as its victim any root-owned process, a kernel thread, or a task that has a hardware device open.

What if we would like to ensure...