Subject: Re: [PATCH] SPARSEMEM + NUMA can't handle unaligned memory regions?
From: Dave Hansen <haveblue@us.ibm.com>
To: Andy Whitcroft <apw@shadowen.org>
Cc: Michael Ellerman <michael@ellerman.id.au>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org, kravetz@us.ibm.com
In-Reply-To: <4460A6F3.5060303@shadowen.org>
References: <20060509070343.57853679F2@ozlabs.org>
	 <44609A7B.7010103@shadowen.org>  <4460A6F3.5060303@shadowen.org>
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Date: Tue, 09 May 2006 09:26:46 -0700
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On Tue, 2006-05-09 at 15:28 +0100, Andy Whitcroft wrote:		
> +/*
> + * During early boot we need to record the nid from which we will
> + * later allocate the section mem_map.  Encode this into the section
> + * pointer.  Overload the section_mem_map with this information.
> + */ 

Andy, this all looks pretty good.  Although, it might be nice to
document this a bit more. 

First, can you update the mem_section definition comment?  It has a nice
explanation of how we use section_mem_map, and it would be a shame to
miss this use.

Also, your comment says when we _record_ the nid information, but not
that it is only _used_ during early boot.  I think this is what Mike K.
missed, and it might be good to clarify.

How about something like this:

/*
 * During early boot, before section_mem_map is used for an actual
 * mem_map, we use section_mem_map to store the section's NUMA
 * node.  This keeps us from having to use another data structure.  The
 * node information is cleared just before we store the real mem_map.
 */

-- Dave

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