Comment 5 for bug 1633161

I am afraid this sounds more like a kernel issue. Please try and updated kernel and see if it fixes it. Similarly, some motherboards try all sorts of tricks to make ram sticks which are different work at the same frequency, but then they give up.

Can you confirm there exists at least a kernel version or distribution of linux where all your 8 gigs are recognized?

Similarly, you can try memtest86.

Otherwise, there isn't much we can do.