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From: Kumar Gala <galak@kernel.crashing.org>
To: Rune Torgersen <runet@innovsys.com>
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Subject: Re: 1 GB lowmem
Date: Wed, 21 May 2008 16:12:40 -0500
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On May 21, 2008, at 3:55 PM, Rune Torgersen wrote:

> Rune Torgersen wrote:
>> linuxppc-dev-bounces+runet=innovsys.com@ozlabs.org wrote:
>>> Hi
>>>
>>> I am trying to enable 1 GB of lowmem on a Freescale 8280.
>>> In arch/ppc this was easilly done by:
>>> CONFIG_ADVANCED_OPTIONS=y
>>> CONFIG_HIGHMEM_START=0xfe000000
>>> CONFIG_LOWMEM_SIZE_BOOL=y
>>> CONFIG_LOWMEM_SIZE=0x40000000
>>> CONFIG_KERNEL_START_BOOL=y
>>> CONFIG_KERNEL_START=0xa0000000
>>>
>>> This does not work in arch/powerpc. CPU hangs as soon as init  
>>> starts.
>>> Any ideas what to look at, what to change?
>>>
>>> The reason I want to do this is because I cannot get highmem support
>>> to work when using CONFIG_PREEMPT_RT.
>>> (hitting a bug_on in kmap_atomic)
>>
>> Scratch that. 1 GB lowmem works with vanilla 2.6.25.4, but
>> not at all with 2.6.25.4-rt[13]
>
> Argh... Found it. Had to set CONFIG_TASK_SIZE to 0x80000000. Now it
> works in both vaniulla an d RT kernel.

We should really add some sanity check on CONFIG_TASK_SIZE vs  
KERNEL_START.

- k