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

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Date:	Thu, 26 Apr 2007 11:13:49 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, Mel Gorman <mel@...net.ie>,
	William Lee Irwin III <wli@...omorphy.com>,
	David Chinner <dgc@....com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Badari Pulavarty <pbadari@...il.com>,
	Maxim Levitsky <maximlevitsky@...il.com>
Subject: Re: [00/17] Large Blocksize Support V3

On Thu, 26 Apr 2007, Nick Piggin wrote:

> > But what do you mean with it? A block is no longer a contiguous section of
> > memory. So you have redefined the term.
> 
> I don't understand what you mean at all. A block has always been a
> contiguous area of disk.

You want to change the block layer to support larger blocksize than 
PAGE_SIZE right? So you need to segment that larger block into pieces.

> > And you dont care about Mel's work on that level?
> 
> I actually don't like it too much because it can't provide a robust
> solution. What do you do on systems with small memories, or those that
> eventually do get fragmented?

You could f.e. switch off defragmentation and the large block support?

> Actually, I don't know why people are so excited about being able to
> use higher order allocations (I would rather be more excited about
> never having to use them). But for those few places that really need
> it, I'd rather see them use a virtually mapped kernel with proper
> defragmentation rather than putting hacks all through the core code.

Ahh. I knew we were going this way.... Now we have virtual contiguous vs. 
physical discontiguous.... Yuck hackidihack.

> > No this has been tried before and does not work. Why should we loose the
> > capability to work with 4k pages just because there is some data that has to
> > be thrown around in quantity? I'd like to have flexibility here.
> 
> Is that a big problem? Really? You use 16K pages on your IPF systems,
> don't you?

Yes but the processor supports 4k also. I'd rather have a choice. 16k is a 
choice for performance given the current kernel limitations hat wastes 
lots of memory.

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