Powered down last night because of an approaching thunderstorm ... half my ram gone again.
disable_mtrr_cleanup did nothing.
disable_mtrr_trim would hang the boot.
I noticed the RAM speed was wrong in the BIOS again so i reset it, and lo and behold it all showed up, but only until the next reboot. Back to bhe BIOS and just changed the ram from one speed to another and back again - RAM returns!