linux-kernel - Re: memory remapping, 4gb memory on 945gt

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Message-ID: <20080104181918.GA21797@gallifrey>
Date:	Fri, 4 Jan 2008 18:19:18 +0000
From:	"Dr. David Alan Gilbert" <linux@...blig.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	felix-linuxkernel@...e.de, linux-kernel@...r.kernel.org
Subject: Re: memory remapping, 4gb memory on 945gt

* Andi Kleen (andi@...stfloor.org) wrote:
> felix-linuxkernel@...e.de writes:
> 
> > I recently put 4 GB of memory in my Acer Travelmate 8210 series
> > notebook.  The BIOS only detects 3 GB.
> 
> Actually it will detect 4GB, but put the PCI hole over the last GB.
> One way to get more usable memory is to configure the BIOS to use a smaller
> PCI hole (e.g. use smaller frame buffer/aperture etc.)

Unfortunately there are certainly some that don't make many options
for configuration and also use a vast amount; my Toshiba A100-306
uses an entire 1GB for the PCI space and has very little in the
way of configuration.

> > I googled around a little.  It appears to be a chipset limitation of the
> > 945gt, which uses the fourth gig for devices.
> >
> > Now I can understand this explanation for 32-bit mode, but I'm running
> > in 64-bit mode.  There should be a way to use the fourth gig under
> > Linux.  Is there?
> 
> The chipset limitation applies to 64bit mode as well as to 32bit mode
> (which actually does not have a 4GB limitation with PAE)

Note that some system and memory vendors have incorrect statements
stating that the 3.xGB limit is a 32bit OS issue on these machines
and it'll all just work fine on 64bit OSs.

Dave
-- 
 -----Open up your eyes, open up your mind, open up your code -------   
/ Dr. David Alan Gilbert    | Running GNU/Linux on Alpha,68K| Happy  \ 
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 \ _________________________|_____ http://www.treblig.org   |_______/
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