ramdisk.rsync OpenRC init script to sync tmpfs directories to hard disk and viceversa on system shutdown and boot respectively. I used on my GNU/Funtoo OS but would also work for GNU/Gentoo users.
This is the line i added to /etc/fstab file:
varcache /var/cache tmpfs size=2048M,noatime,nodiratime,nodev 0 0
Then run sudo mount -a.
Once /var/cache is mounted as tmpfs one can go on with the last step. By default, the scripts uses /home/sys/ramdisk-backup directory to store /var/cache contents when the system goes down so make sure a)the backup directory exists - mkdir -p /home/sys/ramdisk-backup - or b) edit the script and change dst var to your please and then create the desired backup directory.
Just download or clone or the file into /etc/init.d, then chmod +x /etc/init.d/ramdisk.rsync and sudo rc-update add ramdisk.rsync boot.
Lastly, run sudo /etc/init.d/ramdisk.rsync sync && sudo /etc/init.d/ramdisk.rsync start.