Book Image

Mastering Embedded Linux Programming - Second Edition

By : Chris Simmonds
Book Image

Mastering Embedded Linux Programming - Second Edition

By: Chris Simmonds

Overview of this book

Embedded Linux runs many of the devices we use every day, from smart TVs to WiFi routers, test equipment to industrial controllers - all of them have Linux at their heart. Linux is a core technology in the implementation of the inter-connected world of the Internet of Things. The comprehensive guide shows you the technologies and techniques required to build Linux into embedded systems. You will begin by learning about the fundamental elements that underpin all embedded Linux projects: the toolchain, the bootloader, the kernel, and the root filesystem. You’ll see how to create each of these elements from scratch, and how to automate the process using Buildroot and the Yocto Project. Moving on, you’ll find out how to implement an effective storage strategy for flash memory chips, and how to install updates to the device remotely once it is deployed. You’ll also get to know the key aspects of writing code for embedded Linux, such as how to access hardware from applications, the implications of writing multi-threaded code, and techniques to manage memory in an efficient way. The final chapters show you how to debug your code, both in applications and in the Linux kernel, and how to profile the system so that you can look out for performance bottlenecks. By the end of the book, you will have a complete overview of the steps required to create a successful embedded Linux system.
Table of Contents (17 chapters)

Per-process memory usage

There are several metrics to measure the amount of memory a process is using. I will begin with the two that are easiest to obtain: the virtual set size (vss) and the resident memory size (rss), both of which are available in most implementations of the ps and top commands:

  • Vss: Called VSZ in the ps command and VIRT in top, this is the total amount of memory mapped by a process. It is the sum of all the regions shown in /proc/<PID>/map. This number is of limited interest since only part of the virtual memory is committed to physical memory at any time.
  • Rss: Called RSS in ps and RES in top, this is the sum of memory that is mapped to physical pages of memory. This gets closer to the actual memory budget of the process, but there is a problem: if you add the Rss of all the processes, you will get an overestimate of the memory in use because some pages...