I picked up a paper 2nd edition of "Understanding the Linux Kernel" from the free shelf at my local library. It spends about half of the book discussing the 32-bit x86 architecture... The other half is data structures. Very nice index of every system call discussed.

  While ten year old computer books are considered obsolete, systems architecture books may actually be better at documenting the motivation behind design decisions. 

So if you happen upon this discussion thread, you might find it useful.

https://www.oreilly.com/library/view/understanding-the-linux...