Is it possible for two processes to use the same shared-memory without resorting to a file to obtain it, be it a memory-mapped file or /dev/shm file?

I'm curious because today the only way I know how to give two different processes the same shared-memory is through a memory-mapped file, in other words, both processes open the same memory-mapped file and write/read to/from it. That has penalties / drawbacks as the operating system needs to swap between disk and memory. Apologies in advance if that is a silly question, but is there such a thing as a pure shared memory between processes, not backed by a file. If yes, how would the processes get a hold of it if not using a memory-mapped file or /dev/shm file?