mmap is not as free as people think. VM subsystem is full of inefficient locks. Here is a very good writeup on a problem BBC encountered with Varnish: https://www.bbc.co.uk/blogs/internet/entries/17d22fb8-cea2-4...
Interesting. I was aware of various mmap limitations, but I didn’t think about the TLB changes/flushes, which obviously come with an important overhead.