More detailed explanation from ChatGPT. As quick estimate you could achieve a >2x speed up using memory mapped files for a typical assembler workload.
https://chatgpt.com/share/68b5e0db-a6d0-8005-9101-d326d2af0a...
https://chatgpt.com/share/68b5e0db-a6d0-8005-9101-d326d2af0a...
In any case, if you really believe mmap is great for an assembler, then sure, go ahead. But it's not.