Re: [patch 6/12] mm: remove bad_range

Re: [patch 6/12] mm: remove bad_range

[Nick Piggin]

Dave Hansen wrote:

> 
> I seem to also remember a case with this bad_range() check was useful
> for zones that don't have their boundaries aligned on a MAX_ORDER
> boundary.  Would this change break such a zone?  Do we care?
> 

Hmm, I guess that would be covered by the:

         if (page_to_pfn(page) >= zone->zone_start_pfn + zone->spanned_pages)
                 return 1;
         if (page_to_pfn(page) < zone->zone_start_pfn)
                 return 1;

checks in bad_range. ISTR some "warning: zone not aligned, kernel
*will* crash" message got printed in that case. I always thought
that zones were supposed to be MAX_ORDER aligned, but I can see how
that restriction might be relaxed with these checks in place.

This commit introduced the change:
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=commitdiff;h=d60c9dbc4589766ef5fe88f082052ccd4ecaea59

I think this basically says that architectures who care need to define
CONFIG_HOLES_IN_ZONE and handle this in pfn_valid.

Unless this is a very common requirement and such a solution would have
too much performance cost? Anyone?

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