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Date: Sat, 28 Apr 2007 02:58:01 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: David Chinner <dgc@sgi.com>, Christoph Lameter <clameter@sgi.com>,
       linux-kernel@vger.kernel.org, Mel Gorman <mel@skynet.ie>,
       William Lee Irwin III <wli@holomorphy.com>,
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       Badari Pulavarty <pbadari@gmail.com>,
       Maxim Levitsky <maximlevitsky@gmail.com>,
       Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: [00/17] Large Blocksize Support V3
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On Sat, 28 Apr 2007 10:43:28 +0100 Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> On Fri, 27 Apr 2007 21:56:34 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Sat, 28 Apr 2007 13:17:40 +1000 David Chinner <dgc@sgi.com> wrote:
> > 
> > > > Fix up your lameo HBA for reads.
> > > 
> > > Where did that come from? You spend 20 lines described the inefficiencies
> > > of the readahead in the page cache and it should be fixed but then you
> > > turn around and say fix the HBA? 
> > 
> > My (repeated) point is that if we populate pagecache with physically-contiguous 4k
> > pages in this manner then bio+block will be able to create much larger SG lists.
> 
> Also remember that even if you do larger pages by using virtual pairs or
> quads of real pages because it helps on some systems you end up needing
> the same sized sglist as before so you don't make anything worse for
> half-assed controllers as you get the same I/O size providing they have
> the minimal 2 or 4 sg list entries (and those that don't are genuinely
> beyond saving and nowdays very rare)
> 

Could you expand on that a bit please?  I don't get it.