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Re: HIGHMEM

To: Hdei Nunoe <nunoe@co-nss.co.jp>
Subject: Re: HIGHMEM
From: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 15 Dec 2004 15:15:08 +0100
Cc: linux-mips@linux-mips.org
In-reply-to: <001701c4e195$24d48260$3ca06096@NUNOE>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <001101c4dbf9$1da02270$3ca06096@NUNOE> <20041207095837.GA13264@linux-mips.org> <001701c4e195$24d48260$3ca06096@NUNOE>
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User-agent: Mutt/1.4.1i
On Tue, Dec 14, 2004 at 01:26:55PM +0900, Hdei Nunoe wrote:

> >In 2.4 the support for CONFIG_DISCONTIG and CONFIG_NUMA are a bit tangled
> >with each other because IP27 is the only platform to uses these features
> >and it needs both.
> 
> Is it named "sgi-ip27"?

Yes, obviously :-)

> >Other than that you can also just setup your system
> >as 0x0 - 0x10000000 being RAM, 0x10000000 - 0x20000000 being reserved
> >memory and 0x20000000 - 0x30000000 being highmem.  Which works but is a
> >bit wasteful.
> 
> The gap in physical memory is 0x10000000 - 0x20000000, but it is 
> 0x90000000 -
> 0xC0000000 in virtual memory because there is K1 segment.  So the macros 
> such
> as __pa() or __va() does not work, I think.  Started to wonder it might not 
> be easy
> as just changing the PAGE_OFFSET value.  Do you see?

PAGE_OFFSET is the difference of a ZONE_NORMAL's virtual address and it's
physical address.  Once there is no more 1:1 mapping between physical and
virtual addresses such as in your suggestion PAGE_OFFSET can no longer be
used, that is you need to rewrite all users of this function.

  Ralf

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