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 slab shrinkers

Caches are good for performance. Visualize reading the content of a large file from disk as opposed to reading its content from RAM. There's no question that the RAM-based I/O is much faster! As can be imagined, the Linux kernel leverages these ideas and thus maintains several caches – the page cache, dentry cache, inode cache, slab caches, and so on. These caches indeed greatly help performance, but, thinking about it, are not actually a mandatory requirement. When memory pressure reaches high levels (implying that too much memory is in use and too little is free), the Linux kernel has mechanisms to intelligently free up caches (aka memory reclamation - it's a continuous ongoing process; kernel threads (typically named kswapd*) reclaim memory as part of their housekeeping chores; more on this in the Reclaiming memory – a kernel housekeeping task and OOM section).

In the case of the slab cache(s), the fact is that some kernel...