The implementation of switch_root.c inside util-linux prints a warning caused by a check, most likely because it looks for the device number and not the filesystem type. As result some memory will be wasted for the initramfs, which is not needed after booting-up is completed.
* package version(s): util-linux <= 2.24.1-5 and linux >= 3.14
* discussion: https://bbs.archlinux.org/viewtopic.php?id=179422
* proposed patch by Dave Reisner: http://www.spinics.net/lists/util-linux-ng/msg09062.html
Boot system with the implementation of switch_root.c from util-linux
Use implementations from Systemd or BusyBox. Which work in a similiar way like the proposed patch.
Bugreport (Downstream): https://bugs.archlinux.org/task/39734
This doesn't appear to be kernel related