Previously, on OpenRC systems only, the /tmp was mounted as tmpfs only on devices with at least 2 GB of RAM, or when deviceinfo_tmp_as_tmpfs_size was set. On systemd systems, /tmp was unconditionally mounted as tmpfs.
This behavior has recently been reworked, and as part of the rework deviceinfo_tmp_as_tmpfs_size has been removed, as it had an effect only on OpenRC systems, and was not used by any device port in pmaports. User configuration of /tmp is now handled in /etc/conf.d/tmpfs. Users who made use of deviceinfo_tmp_as_tmpfs_size in their /etc/deviceinfo will need to manually set the tmpfs_size configuration option accordingly (as this will not be done automatically).
Additionally, on systemd, /tmp is now mounted only on devices with a sufficient amount of RAM, just like in OpenRC. Configuration is done by adding a unit override of the tmp.mount unit.