To allow configuring the memory limit and human readable (de)serialisation we currently use std::sync::Once:

Once is a low-level primitive and although correct not really the right tool for the job (anymore). Something like OnceLock::get_or_init provides the same functionality as Once + AtomicUsize/Bool in a much nicer API.

But I also think only allowing it to be set once is not necessarily the right thing either. I can imagine a program that might want to increase its limit if it encounters files that are too large iff the computer it's running on has spare resources.