Well, you’ll only understand 100% of it if you’re a kernel developer (and a good one at that). What’s your target? Knowing C and fundamentals of computer architecture + OS design probably gets you to 20-30%. Having spent a bit of time around the Linux kernel itself (writing extensions, drivers, read random blog posts, etc) might get you 60-70%, and so on.
The book you’re reading is very good, your time probably isn’t wasted reading it.
The book you’re reading is very good, your time probably isn’t wasted reading it.