This is dumb, a message from dmesg:
Warning only 896MB will be used. Use a HIGHMEM enabled kernel. 896MB LOWMEM available.Yes, in addition to the old 64M limit and the awkward 4G limit, Linux also has a 896M limit. Why? Beats the hell out of me, but the solution is to rebuild your kernel with the magic CONFIG_NOHIGHMEM parameter where you have three choices: less than 1G, 1-4G, or more than 4G.
I'm sure this has something to do with some hideous aspect of the PC architecture. I really don't care. Couldn't the kernel just figure this out for itself? Ah, but then we wouldn't be l33t linux haqrs.