Not sure why you are downvoted but this is correct, the name Unix is a joke about Multics, which they felt was a bit unwieldy. Unix is a reaction to what they felt was over-wrought operating system design.
In Multics you always mmap'ed files -- that seems crazy to me now that I write asyncio systems inspired by the old mainframe transaction processing systems such as CICS. There is nothing more synchronous, blocking, and dependent on expensive MMU operations than mmap.
MMU operations are a lot more expensive now than they once were.
In particular, one of the most expensive things about mmap today is actually munmap, that trashes the translation lookaside buffer ("TLB"), the cache of memory map lookups, on all the other cores that run threads in the same process. When you had only the one core, that didn't need to happen.
NetBSD used to have "UVM", where they played memory mapping tricks to get "zero-copy" networking. They had to give it up when they went to multiple cores.
Synchronous and blocking is not that bad in timesharing systems, as the computer always has something else to do while it waits for the IO to complete.
As for the expensive MMU operations, as someone pointed out before, they were not always as expensive as we currently have to make them when we need to guard against leaks between processes and multiple CPUs sharing unified memories and caches.
Bell Labs replacing the Outer Space in Plan 9 From Outer Space, a schlocky 1959 sci-fi horror film. The subtitle is UNSPEAKABLE HORRORS FROM OUTER SPACE PARALYZE THE LIVING AND RESURRECT THE DEAD.
Do you have a source for that? Bell Labs Unix had version 9 in 1986 and version 10 in 1989. I suppose it's possible that these happened after Plan 9 was named; but as best as I can tell, work on Plan 9 started in 1987[1]; after V9 Unix had been released.
The Wikipedia's citation on the sentence saying "mid-1980s" is the press release for the 2nd edition of Plan 9 (1995, the first generally available version), which doesn't mention anything of the sort. That is to say: Wikipedia's "mid-1980s" claim isn't well-attributed.
(The 1st edition of Plan 9 (1992) wasn't generally available, and was only made available to universities.)
(My above 1987 citation states that they worked on it in 1987 and implies, but does not explicitly state, that there was no work before that.)
No, really: https://en.wikipedia.org/wiki/Unix