https://web.stanford.edu/class/ee384m/Handouts/HowtoReadPape...

I think this is how we should be reading code as well.

First understand the top level. Then the next level of detail and so on. I treat my understanding as graph of interconnected black boxes. If I don't understand a particular black box or a node in the graph. I click expand on it, grok the details and then collapse the node. Here's the grokking details of a particular sub-node also follows the same structure as understanding the root node. You don't need to understand everything from the get-go, expand your understanding on the need-to-know basis.