Re: 2.6.17-mm1

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Thu, Jun 22, 2006 at 04:54:06PM +0100, Mel Gorman wrote:
> On Thu, 22 Jun 2006, Franck Bui-Huu wrote:
> >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.

Doesn't that result in a massive array of struct pages if your memory
starts a 3GB physical and has 4K pages?  If you have only 32MB in that
scenario, and that was correct, you'd gobble 25MB of that just to
store that array.  Ouch.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
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