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

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Date:	Fri, 27 Apr 2007 20:15:52 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <clameter@....com>
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

Christoph Lameter wrote:
> 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.

The block is the disk block, which does not get segmented.

What you have is a small layer that tells you which block a pagecache
page points to, and which pagecache page refers to a given block. Just
like we have now only slightly extended.


>>>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?

Ahh, then you reboot your machine to access your other filesystems?


>>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.

That gives you have the proper infrastructure that is needed to actually
support higher order _physical_ allocations _properly_.

-- 
SUSE Labs, Novell Inc.
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