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Date: Tue, 15 Apr 2008 10:23:14 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Ingo Molnar <mingo@elte.hu>
cc: Pekka Enberg <penberg@cs.helsinki.fi>, linux-kernel@vger.kernel.org,
       Christoph Lameter <clameter@sgi.com>, Mel Gorman <mel@csn.ul.ie>,
       Nick Piggin <npiggin@suse.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       "Rafael J. Wysocki" <rjw@sisk.pl>, Yinghai.Lu@sun.com
Subject: Re: [bug] SLUB + mm/slab.c boot crash in -rc9
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On Tue, 15 Apr 2008, Ingo Molnar wrote:
> 
> btw., now with a second full day spent on this regression, i have 
> figured out a workaround the hard way: increasing SECTION_SIZE_BITS in 
> include/asm-x86/sparsemem.h from 26 to 27 makes it go away.

Interesting.

I wonder..

So since you don't have NUMA, you have NODES_SHIFT == 0.

That in turn means that NODE_NOT_IN_PAGE_FLAGS is _not_ set.

That, in turn, means that ZONEID_SHIFT does *not* contain SECTIONS_SHIFT.
Is that really what is supposed to happen?

Because then "page_is_buddy()" will not even test the section, as far as I 
can tell.

But I'm probably missing something. Why would we not need to test the 
section in page_zone_id() when the node ID is in the page flags (but has 
zero size)?

		Linus