That reminds me of a custom Linux device driver that I worked with in the past. It implemented "mmap" so that a user application could map a ring buffer into us

That reminds me of a custom Linux device driver that I worked with in the past. It implemented "mmap" so that a user application could map a ring buffer into userspace for zero-copy transfers. It used lazy mapping in the sense that it relied on the page fault handler to get triggered to map each page in as they were touched. This resulted in a latency increase for the very first accesses, but then it was fast after that since the pages stayed mapped in. The solution? Read the entire ring buffer one time during startup to force all pages to get mapped in. I eventually changed the driver to just map them all in at once.