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SubjectRe: 2.6.17-mm1
On Thu, 22 Jun 2006, Franck Bui-Huu wrote:

> Mel Gorman wrote:
>> On Thu, 22 Jun 2006, Franck Bui-Huu wrote:
>>>
>>> Should ARCH_PFN_OFFSET macro be used instead in order to make pfn/page
>>> convertions work when node 0 start offset do not start at 0 ?
>>>
>>
>> What happens if you have ARCH_PFN_OFFSET as
>>
>> #define ARCH_PFN_OFFSET (0UL)
>>
>> ?
>
> It's the default value (see memory_model.h). It means that pfn start
> for node 0 is 0, therefore your physical memory address starts at 0.
>

I know, but what I'm getting at is that ARCH_PFN_OFFSET may be unnecessary
with flatmem-relax-requirement-for-memory-to-start-at-pfn-0.patch applied.
ARCH_PFN_OFFSET is used as

#define page_to_pfn(page) ((unsigned long)((page) - mem_map) + \
ARCH_PFN_OFFSET)

because it knew that the map may not start at PFN 0. With
flatmem-relax-requirement-for-memory-to-start-at-pfn-0.patch, the map will
start at PFN 0 even if physical memory does not start until later.

>>
>> What arch is this?
>>
>
> well I'm working on MIPS, but you can take a look at ARM that does the
> same thing better...
>
>>> My physical memory start at 0x20000000. So node 0 starts at an offset
>>> different from 0. I setup ARCH_PFN_OFFSET this way
>>>
>>> #define ARCH_PFN_OFFSET (0x20000000 << PAGE_SHIFT)
>>>
>>
>> If physical memory starts at 0x20000000, why is the PFN not
>> 0x20000000 >> PAGE_SHIFT ?
>>
>
> It is a typo...
>

ok

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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