Re: [patch 2/2] mm: handle unaligned zones

[Nick Piggin <nickpiggin@yahoo.com.au>]

Mel Gorman wrote:
> On Sun, 21 May 2006, Nick Piggin wrote:
> 
>> Andrew Morton wrote:
>>
>>> How about just throwing the pages away?  It sounds like a pretty rare
>>> problem.
>>
>>
>> Well that's what many architectures will end up doing, yes. But on
>> small or embedded platforms, 4MB - 1 is a whole lot of memory to be
>> throwing away.
>>
>> Also, I'm not sure it is something we can be doing in generic code,
>> because some architectures apparently have very strange zone setups
>> (eg. zones from several pages interleaved within a single zone's
>> ->spanned_pages).
> 
> 
> I looked through a fair few arches code that sizes zones and I couldn't 
> find this or odd calls to set_page_links(). What arch interleaves pages 
> between zones like this? I am taking you mean that you can have a 
> situation where within one contiguous block of pages you have something 
> like;
> 
> dddNNNdddNNNddd
> 
> Where d is a page in ZONE_DMA and N is a page in ZONE_NORMAL.
> 
> The oddest I've seen is where nodes interleave like on PPC64. There you 
> can have pages for node 0 followed by pages for node 1 followed by node 
> 0 again. But the zone start and end pfns stay in the same place.

Depending on how you look, ZONE_DMA and ZONE_NORMAL aren't always "zones" :)

I'm talking about struct zones, rather than zones-as-in-memory-classes.
So yes, PPC64 is my example. Andy's zone index check should take care
of those.

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