linux-kernel - Re: [00/17] Large Blocksize Support V3

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Message-Id: <20070428025801.eca77146.akpm@linux-foundation.org>
Date:	Sat, 28 Apr 2007 02:58:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	David Chinner <dgc@....com>, Christoph Lameter <clameter@....com>,
	linux-kernel@...r.kernel.org, Mel Gorman <mel@...net.ie>,
	William Lee Irwin III <wli@...omorphy.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Badari Pulavarty <pbadari@...il.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [00/17] Large Blocksize Support V3

On Sat, 28 Apr 2007 10:43:28 +0100 Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> On Fri, 27 Apr 2007 21:56:34 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Sat, 28 Apr 2007 13:17:40 +1000 David Chinner <dgc@....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.
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