Unexpected sendFile() performance behavior

Hello, I have been playing around with implementing cat-like utility (mostly to help other people learn). While doing so i encountered interesting performance characteristic of sendFile() on linux. I will focus on the static builds, libC builds just link libC and use its allocator. I am cating a 0.5 GiB file with stdout redirected to a file. I checked that the code does as expected and counted the syscalls used. The code: const std = @import("std"); // this is not 1:1 mapping of th...