linux-kernel - Re: [patch 00/14] Page cache cleanup in anticipation of Large Blocksize support

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Date:	Thu, 14 Jun 2007 22:07:49 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	clameter@....com, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [patch 00/14] Page cache cleanup in anticipation of Large Blocksize support

On Thu, Jun 14, 2007 at 01:06:45PM -0700, Andrew Morton wrote:
> On Thu, 14 Jun 2007 12:38:39 -0700
> clameter@....com wrote:
> 
> > This patchset cleans up the page cache handling by replacing
> > open coded shifts and adds through inline function calls.
> 
> If we never inflict variable PAGE_CACHE_SIZE upon the kernel, these changes
> become pointless obfuscation.
> 
> Let's put our horses ahead of our carts.  We had a lengthy discussion about
> variable PAGE_CACHE_SIZE in which I pointed out that the performance
> benefits could be replicated in a manner which doesn't add complexity to
> core VFS and which provides immediate benefit to all filesystems without
> any need to alter them: populate contiguous pagecache pages with physically
> contiguous pages.
> 
> I think the best way to proceed would be to investigate that _general_
> optimisation and then, based upon the results of that work, decide whether
> further _specialised_ changes such as variable PAGE_CACHE_SIZE are needed,
> and if so, what they should be.

Christophs patches are an extremly useful cleanup and can stand on their
own.  Right now PAGE_CACHE_SIZE and friends are in there and now one can
keep them distinct because their useage is not clear at all.  By making
the macros per-mapping at least the useage is clear.

That beeing said we should do a full conversion so that PAGE_CACHE_SIZE
just goes away, otherwise the whole excercise is rather pointless.
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