linux-kernel - Re: 4Gb ram not showing up

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Date:	Mon, 4 Jun 2007 18:28:40 -0400
From:	Wakko Warner <wakko@...mx.eu.org>
To:	Tom Moore <tmoore@...tial.ca>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: 4Gb ram not showing up

Tom Moore wrote:
> Thank you for the reply back.  Your answer makes perfect sense to me, 
> and it is what I had suspected but was not sure about.  The math seems 
> to indicate that 4Gb of ram plus 1Gb of PCI address space equals 5Gb of 
> memory space.  So it does sound like I should have a larger kernel model.
> 
> What confused me the most (and still does), is the help message string 
> that is presented for the CONFIG_HIGHMEM4G option:
>  "Select this if you have a 32-bit processor and between 1 and 4 
> gigabytes of physical RAM."

4 is not between 1 and 4.

> Well that sounds like the amount of memory that I have, so that is what 
> I selected.

You should select CONFIG_HIGHMEM64G.

> Also, although I know what PAE stands for, I don't know how to select it 
> when building a kernel.  Would I get this from the CONFIG_HIGHMEM64G 
> option?  The help text for that says:
>  "Select this if you have a 32-bit processor and more than 4 gigabytes 
> of physical RAM."

Personally, I feel the wording should say:
Select this if you have a 32-bit processor and 4 or more gigabytes of
physical RAM.

It may not hurt to say 3 or more, but I'm not that familiar with x86
hardware in regards to memory.

> This does not sound like it applies to my hardware.  There is something 
> wrong with my understanding, or with these message strings.  I am still 
> confused.

It does.

Here's my system (4gb of memory):
             total       used       free     shared    buffers     cached
Mem:       3619996    3289352     330644          0     469764    2025416
-/+ buffers/cache:     794172    2825824
Swap:            0          0          0

I know it says 3.6gb of memory, but 4gb is installed.  I had 5gb in this
machine and I saw all 5gb.  This is a 32-bit dual xeon (12gb max memory)

I would be interested to know where the last 400mb of memory went.

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