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Re: [vox-tech] Kernel not seeing all my RAM
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Re: [vox-tech] Kernel not seeing all my RAM

On Tue, 2009-02-03 at 10:28 -0800, Bill Broadley wrote:
> Chanoch (Ken) Bloom wrote:
> > I'm upgrading an x86
> Not x86-64?

There's two machines with this problem. One is really an x86. The other
is an amd64, but it's running a totally 32-bit system since it shares
home directories by NFS with the first machine (and a couple other
32-bit only machines).

With regard to the amd64, I'd like to have it run a 64-bit kernel with a
32-bit userspace, but the machines are running Gentoo, and I don't know
how to do that in Gentoo.

(I'm looking at switching these machines to Debian in the long run, and
I'll probably start testing that on one machine after lenny is released
in a couple weeks, so in the long run I may not need to solve the
kernel/userspace thing in Gentoo.)

> > machine to 4 GB of RAM, and have compiled the
> > kernel with CONFIG_HIGHMEM64G=y, but the kernel is only seeing 3283 MB
> > of the RAM. Any idea what I'm doing wrong?
> Nothing.  It's up to the motherboard to remap memory reserved for I/O to
> memory over 4GB.  Thinks like a 256MB video card often require 768MB of
> address space.
> Check out BIOS for any hint of being able to remap memory, high memory, bounce
> buffers for I/O, etc.

So you're saying that a 32-bit kernel will map devices in into the 4GB
address space in such a way that they hide physical RAM, regardless of
whether you're using CONFIG_HIGHMEM4G or CONFIG_HIGHMEM64G, and that a
64-bit kernel will map devices differently. Is this right?


Ken (Chanoch) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.

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