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SubjectRe: Accessing more than 2GB of memory with a 32 bit kernel
On 06/12/2013 10:10 PM, Rik van Riel wrote:
> On 06/12/2013 12:54 PM, Simon Brown wrote:
>> Hello,
>>
>> For the sake of an old prototype peripheral I'm using a non PAE 32 bit
>> x86 kernel and I'm having trouble accessing memory above 2 GB. The
>> system has 4GB installed and all is well with a PAE kernel.
>>
>> I'm obviously expecting to lose some memory due to memory mapped devices
>> but I wasn't expecting to lose 2GB. Instead I'm suspecting a BIOS bug.
>> The system reports:
>> free -m
>> total used free shared buffers
>> cached
>> Mem: 2012 491 1521 0 40
>> 277
>>
>> The mtrr table looked odd so I enabled sanitisation:
>> [ 0.000000] original variable MTRRs
>> [ 0.000000] reg 0, base: 2GB, range: 2GB, type UC
>> [ 0.000000] reg 1, base: 0GB, range: 4GB, type WB
>> [ 0.000000] reg 2, base: 4GB, range: 2GB, type WB
>> [ 0.000000] total RAM covered: 4096M
>> [ 0.000000] Found optimal setting for mtrr clean up
>> [ 0.000000] gran_size: 64K chunk_size: 64K num_reg: 2
>> lose cover RAM: 0G
>> [ 0.000000] New variable MTRRs
>> [ 0.000000] reg 0, base: 0GB, range: 2GB, type WB
>> [ 0.000000] reg 1, base: 4GB, range: 2GB, type WB
>>
>> I don't understand the gap in the new table.
>
> Check the e820 table. Chances are the BIOS is reserving 2GB to
> map various devices (especially video cards) below the 4GB limit.
>
>

Acording to manual, that mobo has an option to "Memory remap feature"
in BIOS that looks like that...

--
J.A. Magallon <jamagallon()ono!com> \ Winter is coming...


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