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

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Message-ID: <20070424230046.GH11166@waste.org>
Date:	Tue, 24 Apr 2007 18:00:46 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	Mel Gorman <mel@...net.ie>, 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 Fri, Apr 20, 2007 at 12:10:43PM -0700, Christoph Lameter wrote:
> On Fri, 20 Apr 2007, Dave Kleikamp wrote:
> 
> > On Fri, 2007-04-20 at 12:05 +0100, Mel Gorman wrote:
> > 
> > > comments about missing page_cache_size() covered elsewhere. However, I
> > > note that Dave Kleikamp might be interested in this changing of
> > > page_cache_size() from the perspective of page cache tails. I've added
> > > him to the cc so he can take a quick look.
> > 
> > Yeah.  I'm working on patches for storing file tails in buffers
> > allocated from the slab cache, and the tail will be represented by a
> > fake struct page.  (This is primarily for kernels with a larger page
> > size).  So my version of page_cache_size(page) may return a different
> > size for different pages belonging to the same mapping.  I'm in the
> > midst of cleaning up the patches and plan to post them to linux-mm by
> > Monday.
> 
> I am not sure what the point of that patchset would be in this context 
> given that this is about support for arbitrary page sizes. If the 
> filesystem wants it then it can reduce the page size for small files.

Shaggy's suggestion is to emulate pages with _negative_ orders.

-- 
Mathematics is the supreme nostalgia of our time.
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