Does named shared memory imply IO and impact the performance?

Question

I need to share many memory buffers between two processes. I'm trying to use mmap to archive it. According to the doc, only with the MAP_ANONYMOUS flag, no file descriptor is needed, therefore I wouldn't worry about physical IO taking place.

But anonymous mapping only can be used within single process, I need some names to identify each buffer between processes! Therefor I have to use shm_open to create a file descriptor before calling mmap.

After calling shm_open, a file would appear at /dev/shm, I'm worrying about that some disk IO invoked. I know that is a temporary file system, but I'm confusing where it is stored at last?

Is there another way, we can create Named Shared Memory without a file in Linux?

In addition, I need "lazy-allocation" and "full-zero initialization". I'm interested in whether those still be guaranteed with "Named Shared Memory" or not.