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 18:51:36 +0200
From:	Jens Axboe <jens.axboe@...cle.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 Fri, Apr 20 2007, Christoph Lameter wrote:
> On Fri, 20 Apr 2007, Jens Axboe wrote:
> 
> > This works fine as long as you are in the submitter context, but once
> > you pass the into the block layer, we don't have any way to find the
> > address space (at least we don't want to). Would something like this be
> > workable, name withstanding:
> > 
> > static unsigned long page_size(struct page *page)
> > {
> >         struct address_space *mapping;
> >         int order = 0;
> > 
> >         mapping = page_mapping(page);
> >         if (mapping)
> >                 order = mapping->order;
> > 
> >         return PAGE_CACHE_SIZE << order;
> > }
> 
> There is much simpler solution (possible with mm)
> 
> PAGE_SIZE << compound_order(page)
> 
> compound_order will return 0 for a non compound page.

Ah perfect, much easier. I'll spin a patchset for the block bits.

-- 
Jens Axboe

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