Re: [RFC][PATCH] remove zone_mem_map [3/4] pfn_to_page()

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

Martin J. Bligh wrote:
> KAMEZAWA Hiroyuki wrote:
>> Replace page_to_pfn() functions which uses zone->zone_mem_map.
>>
>> Although pfn_to_page() uses node->node_mem_map, page_to_pfn() uses
>> zone->zone_mem_map. I don't know why. This patch make page_to_pfn
>> use node->node_mem_map
> 
> I think that might have been because it's a faster op, at least on
> some architectures, under sparsemem. Andy, can you confirm / deny?
> Some part of the mapping was embedded in the page flags.
> 
Under sparsemem, zone->zone_mem_map is meaningless.
The mem_map is not contiguous.

If NODE_DATA(nid) is slower than page_zone() , this change will be problem.
While page_zone() accesses global zone_table[], NODE_DATA(nid) depends on each
arch. Some archs has local NODE_DATA table.

> If Andy can't recall, I'll look again on Thursday when I'm back ...
> 
> M.
> 
Thank you!.

-Kame

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