I remember this too. Very early on there were both proc and a /dev/kmem versions of ps and maybe top too.

Yep, found it: https://www.ibiblio.org/pub/historic-linux/ftp-archives/suns...

And the Linux kernel CREDITS file has an entry mentioning it too:

    N: Rick Sladkey
    D: utility hacker: Emacs, NFS server, mount, kmem-ps, UPS debugger, strace, GDB
    [...]