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

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Message-ID: <4631CBA6.3090902@yahoo.com.au>
Date:	Fri, 27 Apr 2007 20:08:38 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <clameter@....com>
CC:	David Chinner <dgc@....com>,
	"Eric W. Biederman" <ebiederm@...ssion.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>
Subject: Re: [00/17] Large Blocksize Support V3

Christoph Lameter wrote:
> On Thu, 26 Apr 2007, Nick Piggin wrote:
> 
> 
>>Christoph Lameter wrote:
>>
>>>On Thu, 26 Apr 2007, Nick Piggin wrote:
>>>
>>>
>>>
>>>>But I maintain that the end result is better than the fragmentation
>>>>based approach. A lot of people don't actually want a bigger page
>>>>cache size, because they want efficient internal fragmentation as
>>>>well, so your radix-tree based approach isn't really comparable.
>>>
>>>
>>>Me? Radix tree based approach? That approach is in the kernel. Do not create
>>>a solution where there is no problem. If we do not want to support large
>>>blocksizes then lets be honest and say so instead of redefining what a block
>>>is. The current approach is fine if one is satisfied with scatter gather and
>>>the VM overhead coming with handling these pages. I fail to see what any of
>>>what you are proposing would add to that.
>>
>>I'm not just making this up. Fragmentation. OK?
> 
> 
> Yes you are. If you want to avoid fragmentation by restricting the OS to 
> 4k alone then the radix tree is sufficient to establish the order of pages 
> in a mapping. The only problem is to get an array of pointers to a 
> sequence of pages together by reading through the radix tree. I do not 
> know what else would be needed.

No. We have avoided fragmentation up until now. We avoid fragmentation like
the plague because it is crap. What _I_ do not want to do is add some
patches that make it work a bit better and everyone think's that's a signal
that it is a good idea to start using higher order allocations wherever
possible.

-- 
SUSE Labs, Novell Inc.
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