Re: Memory defined at boot time incorrect

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Wed, Feb 05, 2020 at 09:24:01PM -0700, Andy Ruhl wrote:
> At boot time only about 2 gigs of memory is being discovered, even
> though 4 gigs is installed. I see some options in the kernel config to
> define the memory size but so far I haven't figured out the right
> combination of settings, everything I've tried causes compile errors.

On x86, memory is not always mapped physically continously. If you have
more than 3GB RAM, it will definitely put a hole before 4GB, so that
32bit operating systems can use memory mapped IO for access PCI devices
etc. Where exactly that border is depends on the mainboard, having 2GB
reserved isn't that strange either. The config option is to ensure no
memory is used above certain addresses, e.g. to deal with very limited
DMA engines that can only handle 31bit addresses.

Joerg