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Subject: Re: [RFC][PATCH 2/6] pagewalk: only split huge pages when necessary
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: David Rientjes <rientjes@google.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Michael J Wolf <mjwolf@us.ibm.com>,
        Andrea Arcangeli <aarcange@redhat.com>
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Date: Fri, 04 Feb 2011 09:19:12 -0800
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On Thu, 2011-02-03 at 13:46 -0800, David Rientjes wrote:
> > Probably, but we don't currently have any central documentation for it.
> > Guess we could make some, or just ensure that all the users got updated.
> > Any ideas where to put it other than the mm_walk struct?
> 
> I think noting it where struct mm_walk is declared would be best (just a 
> "/* must handle pmd_trans_huge() */" would be sufficient) although 
> eventually it might be cleaner to add a ->pmd_huge_entry(). 

For code maintenance, I really like _not_ hiding this in the API
somewhere.  This way, we have a great, self-explanatory tag wherever
code (possibly) hasn't properly dealt with THPs.  We get a nice,
greppable, cscope'able:

	split_huge_page_pmd()

wherever we need to "teach" the code about THP.

It's kinda like the BKL. :)

-- Dave