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Re: MIPS 64?

To: Daniel Jacobowitz <dan@debian.org>
Subject: Re: MIPS 64?
From: Jun Sun <jsun@mvista.com>
Date: Wed, 15 May 2002 14:59:34 -0700
Cc: Matthew Dharm <mdharm@momenco.com>, Linux-MIPS <linux-mips@oss.sgi.com>
References: <NEBBLJGMNKKEEMNLHGAIOEPPCGAA.mdharm@momenco.com> <20020515214818.GA1991@nevyn.them.org>
Sender: owner-linux-mips@oss.sgi.com
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Daniel Jacobowitz wrote:

On Wed, May 15, 2002 at 02:34:47PM -0700, Matthew Dharm wrote:

So... I'm looking at porting Linux to a system with 1.5GiB of RAM.
That kinda blows the 32-bit MIPS port option right out of the water...


Not unless you count bits differently than I do... 32-bit is 4 GiB.  Is
there any reason MIPS has special problems in this area?



MIPS has lower 2GB fixed for user space. Then you have kseg0, .5GB for cached physical address 0-0.5GB, and kseg1, 0.5GB uncached mapping of the same area. You can map another 1GB of RAM into kseg2/3, but you will then have no space left for IO.

So you really can't do 1.5GB on 32 bit kernel.

It is interesting that PPC allows one to adjust user space size and kernel space size. So on PPC you can get up to 2.5GB system RAM with 1GB user space.

Back to 64bit port, it seems to me much of the 32bit work we have done in the past a year or so needs to be moved over. Or better yet, if we can clean up integer/long issues, we might be able to use 32bit kernel code straight for 64bit kernel.


Jun



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