linux-kernel - Re: [patch 01/14] Define functions for page cache handling

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Date:	Thu, 14 Jun 2007 21:56:46 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	clameter@....com
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [patch 01/14] Define functions for page cache handling

On Thu, Jun 14, 2007 at 12:38:40PM -0700, clameter@....com wrote:
> We use the macros PAGE_CACHE_SIZE PAGE_CACHE_SHIFT PAGE_CACHE_MASK
> and PAGE_CACHE_ALIGN in various places in the kernel. Many times
> common operations like calculating the offset or the index are coded
> using shifts and adds. This patch provides inline function to
> get the calculations accomplished in a consistent way.
> 
> All functions take an address_space pointer. The address space pointer
> will be used in the future to eventually support a variable size
> page cache. Information reachable via the mapping may then determine
> page size.
> 
> 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_index(a, pos)	Calculate page number from position
> page_cache_next(addr, pos)	Page number of next page
> page_cache_offset(a, pos)	Calculate offset into a page
> page_cache_pos(a, index, offset)
> 				Form position based on page number
> 				and an offset.
> 
> This provides a basis that would allow the conversion of all page cache
> handling in the kernel and ultimately allow the removal of the PAGE_CACHE_*
> constants.

We need access to PAGE_SIZE in vmlinux.lds.h.
What is your plan with that usage?

	Sam
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