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Re: Using more than 256 MB of memory on SB1250 in 32-bit mode

To: linux-mips@linux-mips.org
Subject: Re: Using more than 256 MB of memory on SB1250 in 32-bit mode
From: Daniel Walton <dwalton+mips@ddtsm.com>
Date: Thu, 20 May 2004 16:27:04 -0400
In-reply-to: <20030831133434.GA23189@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <3F4FCCD5.1000604@tadpole.com> <20030831133434.GA23189@linux-mips.org>
Reply-to: Daniel Walton <dwalton+mips@ddtsm.com>
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User-agent: Mutt/1.5.5.1+cvs20040105i
On Sun, Aug 31, 2003 at 03:34:34PM +0200, Ralf Baechle wrote:
> The explanation you gave isn't exactly right.  A 2GB/2GB split would normally
> support 2GB of low memory.  We don't on MIPS due to the very inconvenient and
> unchangable mappings of KSEG0/KSEG1 - something that may have been sweet
> in '85 when the address map was designed but not today when 32-bit address
> spaces are beginning to be fairly tight.
> 
> Highmem works ok in 2.4 as long as you have a reasonably low ratio of
> highmem to lowmem.  For typical loads that means going beyond 4:1 isn't
> sensible but the actual number may vary much based on exact system
> configuration or workload.
> 
>   Ralf
> 

So what is a practical limit to total memory.

Daniel

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