Comment # 21 on bug 1137748 from Franck Bui

(In reply to Hubert Mantel from comment #19)
> Terra:~ # echo -n mem >/sys/power/state
> -bash: echo: write error: Device or resource busy

Ok then it's definitively not due to systemd but something in the lower layer
(kernel, ACPI, BIOS...).

Kernel team, could you have look ?