linux-kernel - Re: [RFC][PATCH 2/6] pagewalk: only split huge pages when necessary

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Date:	Fri, 04 Feb 2011 09:19:12 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael J Wolf <mjwolf@...ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC][PATCH 2/6] pagewalk: only split huge pages when necessary

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

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