동일한 tmpfs를 여러 번 마운트하는 기능

왜 다음과 같은 상황이 가능한가?

root@pkara-pc01:~# mkdir -p /tmp/shared
root@pkara-pc01:~# mount -t tmpfs -o size=1G mymount /tmp/shared/
root@pkara-pc01:~# mount -t tmpfs -o size=1G mymount /tmp/shared/
root@pkara-pc01:~# mount | grep -i shared
mymount on /tmp/shared type tmpfs (rw,relatime,size=1048576k)
mymount on /tmp/shared type tmpfs (rw,relatime,size=1048576k)

편집하다: 일반적으로 이미 마운트된 파일 시스템을 마운트하려고 하면 실패(?)하기 때문에 이 질문을 드립니다.

$ mkdir -p mydir
/tmp
$ dd if=/dev/zero of=myfile bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB, 1000 MiB) copied, 0.563994 s, 1.9 GB/s
/tmp
$ mkfs.ext4 myfile 
mke2fs 1.44.1 (24-Mar-2018)
Discarding device blocks: done                            
Creating filesystem with 256000 4k blocks and 64000 inodes
Filesystem UUID: 95fe153e-a575-4c9a-beef-b7a20a6ae342
Superblock backups stored on blocks: 
    32768, 98304, 163840, 229376

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

/tmp
$ sudo mount -o loop myfile /tmp/mydir/
/tmp
$ sudo mount -o loop myfile /tmp/mydir/
mount: /tmp/mydir/: /tmp/myfile is already mounted.