The kernel usually mounts the root filesystem at the very end of the boot sequence.
It is usually mounted readonly and irrespective of whatever mount option set as part of the
Control is then, given to the init system.
As specified in the manual you linked to,
ignores normal file systems and only changes the root
file system (i.e. /), /usr/, and the virtual kernel API file systems
such as /proc/, /sys/ or /dev/.
You can also read that this service :
is usually pulled in by systemd-fstab-generator
systemd-fstab-generator is in fact responsible for instantiating the initial mount of filesystems according to fstab entries.
This will instantiate mount and swap units as necessary.
It is therefore normal that if you inhibit the automatic execution of systemd-remount-fs.service and reboot, you'll still see your filesystems mounted according to the