[tremon]

Why do you say that reads and writes may also block?

Let's define "may block" first, perhaps? What do we mean when we say "network I/O may block"? Usually, this means that the kernel may see your network request and raise you a context switch while it waits for the network response on your behalf. In your last sentence you appear to argue that the reason why the kernel performs a context switch is relevant in determining if an operation "may block", and the GP is arguing that that's a distinction without a difference.

If the definition of "may block" is really just "the kernel may decide to context-switch away from your program", then yes, the GP's assertion that file I/O, memory I/O (mmap) and memory access (swap) are all operations that may block is correct -- the only difference is in degree: from microsecond delays for nvm-backed swap to multi-second delays for network transfers.

Or, of course, I may have misunderstood the GP's train of thought.