linux-kernel - Re: [PATCH 1/3] add pfn_valid_within helper for sub-MAX

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Date:	Wed, 21 Mar 2007 16:46:33 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Andy Whitcroft <apw@...dowen.org>, Mel Gorman <mel@....ul.ie>,
	Bob Picco <bob.picco@...com>,
	Dave Hansen <hansendc@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] add pfn_valid_within helper for sub-MAX_ORDER hole
 detection

On Thu, 22 Mar 2007 10:23:27 +1100
Nick Piggin <nickpiggin@...oo.com.au> wrote:

> Andy Whitcroft wrote:
> > Generally we work under the assumption that memory the mem_map
> > array is contigious and valid out to MAX_ORDER_NR_PAGES block
> > of pages, ie. that if we have validated any page within this
> > MAX_ORDER_NR_PAGES block we need not check any other.  This is not
> > true when CONFIG_HOLES_IN_ZONE is set and we must check each and
> > every reference we make from a pfn.
> > 
> > Add a pfn_valid_within() helper which should be used when scanning
> > pages within a MAX_ORDER_NR_PAGES block when we have already
> > checked the validility of the block normally with pfn_valid().
> > This can then be optimised away when we do not have holes within
> > a MAX_ORDER_NR_PAGES block of pages.
> 
> Nice cleanup. Horrible name ;) Calls read like "is the pfn valid
> within pfn".

yeah
 
> I can't think of anything really good, but I think, say,
> pfn_valid_within_block or pfn_valid_within_valid_block would be a
> bit better. You still get a slight net savings in keystrokes!

Neither of those identifiers seem to really fit, and I can't think of anything
suitable either.  Oh well, at least pfn_valid_within() has a nice comment
explaining what it does.
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