There are so many complaints here about how simplistic this is and how it is nowhere near what a "good" malloc does. That's kind of the point. Let's implement the most brain-dead version of this code. This is code you can quickly understand and reason about. It gives you a baseline to understand all the improvements that are included in a "real" malloc.

It would have been nice to include a list of the types of changes that a modern malloc would make to this basic structure to make it faster or fix bugs.