linux-kernel - Re: [RFC 4/8] Enhance fallback functions in libs to support higher order pages

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Date:	Fri, 20 Apr 2007 08:50:12 +1000
From:	David Chinner <dgc@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	Adam Litke <aglitke@...il.com>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <nickpiggin@...oo.com.au>, Andi Kleen <ak@...e.de>,
	Paul Jackson <pj@....com>, Dave Chinner <dgc@....com>
Subject: Re: [RFC 4/8] Enhance fallback functions in libs to support higher order pages

On Thu, Apr 19, 2007 at 12:10:34PM -0700, Christoph Lameter wrote:
> Variable Order Page Cache: Add functions to establish sizes
> 
> We use the macros PAGE_CACHE_SIZE PAGE_CACHE_SHIFT PAGE_CACHE_MASK
> and PAGE_CACHE_ALIGN in various places in the kernel. These are now
> the base page size but we do not have a means to calculating these
> values for higher order pages.
> 
> Provide these functions. An address_space pointer must be passed
> to them.
> 
> New function			Related base page constant
> ---------------------------------------------------
> page_cache_shift(a)		PAGE_CACHE_SHIFT
> page_cache_size(a)		PAGE_CACHE_SIZE
> page_cache_mask(a)		PAGE_CACHE_MASK
> page_cache_align(addr,a)	PAGE_CACHE_ALIGN(addr)

I think PAGE_CACHE_SIZE is a redundant define with these
modifications.  The page cache size in now variable and it is based
on a multiple of PAGE_SIZE. Hence I suggest that PAGE_CACHE_SIZE and
it's derivitives should be made to go away completely with this
change.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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