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

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Message-ID: <20070420082129.GI6525@kernel.dk>
Date:	Fri, 20 Apr 2007 10:21:29 +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 Thu, Apr 19 2007, Christoph Lameter wrote:
> +static inline int page_cache_shift(struct address_space *a)
> +{
> +	return a->order + PAGE_CACHE_SHIFT;
> +}
> +
> +static inline unsigned long page_cache_size(struct address_space *a)
> +{
> +	return PAGE_CACHE_SIZE << a->order;
> +}

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;
}

-- 
Jens Axboe

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