linux-kernel - Re: reserve memory in low physical address

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Message-ID: <45474585.2070607@compro.net>
Date:	Tue, 31 Oct 2006 07:45:57 -0500
From:	Mark Hounschell <markh@...pro.net>
To:	Jun Sun <jsun@...sun.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: reserve memory in low physical address - possible?

Jun Sun wrote:
> This question is specific to i386 architecture.  While I am fairly 
> comfortable with Linux kernel, I am not familiar with i386 arch. 
> 
> My objective is to reserve, or hide from kernel, some memory space in low
> physical address range starting from 0.  The memory amount is in the order
> of 100MB to 200MB.  The total memory is assumed to be around 512MB.
> 
> Is this possible?
> 
> I understand it is possible to reserve some memory at the end by
> specifying "mem=xxxM" option in kernel command line.  I looked into
> "memmap=xxxM" option but it appears not helpful for what I want.
> 
> While searching on the web I also found things like DMA zone and loaders
> etc that all seem to assume the existence low-addressed physical
> memory.  True?
> 
> I can certainly workaround the loader issue.  I can also re-code the real-mode
> part of kernel code to migrate to higher addresses.  The DMA zone might be
> a thorny one.  Any clues?  Are modern PCs still subject to
> the 16MB DMA zone restriction?
> 
> Am I too far off from what I want to do?
> 
> Thanks.
> 
> Jun

Maybe the bigphysarea patch is what you want?

Mark

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