To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: Patch to reorder functions in the vmlinux to a defined order
Date: Tue, 7 Mar 2006 15:36:00 -0800 (PST)
Organization: Mostly alphabetical, except Q, with we do not fancy
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References: <1140700758.4672.51.camel@laptopd505.fenrus.org> <m17j7kda52.fsf@ebiederm.dsl.xmission.com> <Pine.LNX.4.64.0602240925170.3771@g5.osdl.org> <43FF48F2.70508@keyaccess.nl>
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Followup to:  <43FF48F2.70508@keyaccess.nl>
By author:    Rene Herman <rene.herman@keyaccess.nl>
In newsgroup: linux.dev.kernel
>
> Linus Torvalds wrote:
> 
> > The real issue is the _physical_ address. Nothing else matters.
> > 
> > If the TLB splitting on the fixed MTRRs is an issue, it depends entirely 
> > on what physical address the kernel resides in, and the virtual address is 
> > totally inconsequential.
> > 
> > So playing games with virtual mapping has absolutely no upsides, and it 
> > definitely has downsides.
> 
> The notion was that having a fixed virtual mapping of the kernel would 
> allow it to be loaded anywhere physically without needing to do actual 
> address fixups. The bootloader could then for example at runtime decide 
> to load the kernel at 16MB if the machine had enough memory available, 
> to free up ZONE_DMA. Or not do that if running on a <= 16MB machine.
> 

The only machines on which ZONE_DMA matters (machines with ISA DMA
devices) are also the ones which are likely to be <= 16 MB.

Yes, there are floppies, but I think having over 3 MB available for
floppy DMA is plenty, and floppies are FINALLY going away...

	-hpa
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