While I had a neutral experience with the interview, I think the interviewers from FB did everything they could to make it pleasant for me.

A recruiter from FB contacted me via LinkedIn. We had a chat over the phone, and she asked me about a couple of available dates after mentioning that there would be two portions of pre-screen interviews: coding and systems. I took about 4 weeks for preparation.

Both the coding and systems interviews were scheduled on the same day.

The coding interview was relatively not hard. You will need to know basic loops, some data structures (especially those that eliminate duplicates and are capable of keeping a set of values related to other values), and some sorting algorithms will be helpful.

The systems interview was relatively hard. I noticed it was split into three parts:

1. Validation of the candidate's solid knowledge of one of the topics. In my case, it was memory management.
2. Practical implementation of part 1 – processes and what they do with memory, how, and why, and what commands in C there are, and so on and so forth. There will be a minimum of 350 pages of reading from Tanenbaum required to pass these parts. I suppose they ask about other topics as well, summing up the overall reading to approximately 1000 pages.
3. The last part of the systems interview was to troubleshoot a system that was running "slow" – a "what would you do" type of question.

Count words and output the top N.

What is such-and-such memory? What data structures do we use? What command would you use to create a process in such-and-such memory?

Why would a process die or not die?

Kill vs. Term: how will you do it in C?