With devpi-server I can now confirm a memory leak somehow related to waitress. I observed it on Debian and FreeBSD, but not on macOS. The last test I did was replacing waitress with cheroot and the leak is completely gone with that. I'm currently working on creating a minimal example for reproduction, but wanted to give a heads up in case someone else noticed something and started investigating. It is certainly possible it is related in how we use waitress in devpi-server, but I don't think we do anything special. I don't want to switch to cheroot, because it lacks some features and seems to be less performant.