I asked Linux for one 4 KiB page from the start of a cold file. Four pages came back.

I moved the same read one page further in, ran it again, and got one.

Same file, same syscall, same kernel. The only thing that changed was where I started

reading, and I spent twenty minutes assuming the tool I'd just written was miscounting.

It wasn't. A read that starts at byte zero is treated as a promise. There's a branch in