Re: 2.6.17-mm1

[Franck Bui-Huu <fbh.work@gmail.com>]

Mel Gorman wrote:
> 
> Architectures will not always have a known fixed start of physical
> memory. On IA64 at least, they initialise memory as if it starts at 0
> but on my one test machine, the beginning part is always a memory hole.

in that case ARCH_PFN_OFFSET is 0 which is the old behaviour, nothing
change...

> I've seen nothing to indicate that this hole will be the same size on
> all IA64 machines but I kinda doubt it. Also, arches that use
> init_bootmem() do not necessary use free_area_init().
> 

but in that case do they use ARCH_PFN_OFFSET != 0 ? if so that would be
very surprising. That would meand "I have a hole a the start of my mem,
I don't know at compile time where it starts, but I state that my physical
mem start at ARCH_PFN_OFFSET anyways"

>> If we don't change init_bootmem() to use ARCH_PFN_OFFSET, then the
>> kernel will initialise the start of memory to 0 which is boggus.
>> IOW,
>> we can't use this function without this change (except if your memory
>> start at 0 of course). And I think that init_bootmem() has been
>> implemented for systems which have only one node _whatever_ memory
>> start value...
>>
> 
> While you may be right, it'll only fix the problem for arches with
> ARCH_PFN_OFFSET and using init_bootmem (which is the case of MIPS I
> guess). But arches using init_bootmem_node or not using free_area_init()
> may still get kicked.
> 

Again in these cases, I doubt that they will setup ARCH_PFN_OFFSET...

		Franck
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