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Re: how to support more than 512MB RAM for MIPS32 ?

To: Ralf Baechle <>
Subject: Re: how to support more than 512MB RAM for MIPS32 ?
From: "Figo.zhang" <>
Date: Thu, 26 Nov 2009 00:17:01 +0800
Cc: Kevin Hickey <>,
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On Wed, 2009-11-25 at 16:00 +0000, Ralf Baechle wrote:
> On Wed, Nov 25, 2009 at 11:31:14PM +0800, Figo.zhang wrote:
> > how to do map extra RAM to any ouside I/O space?
> > it is just motify:
> > 
> > 1. arch/mips/kernel/setup.c: bootm_init()function, motity the define
> > "HIGHMEM_START", for me: 
> > #define HIGHMEM_START 0x2000,0000   //512MB
> Leave HIGHMEM_START unchanged; it should always be 512MB no matter what
> the actual memory addresses of a particular platform are.  The kernel
> needs to treat anything above 512MB differently because it's not
> permanently mapped and HIGHMEM_START stands for this limit.

HIGHMEM canot directly invoke __get_free_pages() to allocate pages, so
it would slow performance ?

Is it anyother solution in current linux-mips kernel? for example,
directly map extra RAM to 0x40000000~0x80000000, the user space
decreased, only 0x0~0x40000000.


>   Ralf

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