Re: 2.6.17-mm1

[Mel Gorman <mel@csn.ul.ie>]

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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