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

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Date:	Thu, 26 Apr 2007 17:48:12 +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:
> 
> 
>>No I don't want to add another fs layer.
> 
> 
> Well maybe you could explain what you want. Preferably without redefining 
> the established terms?

Support for larger buffers than page cache pages.


>>I still don't think anti fragmentation or defragmentation are a good
>>approach, when you consider the alternatives.
> 
> 
> I have not heard of any alternatives in this discussion here. Just the old 
> line of lets tune the VM here and there and hope it lasts a while longer.

I didn't realise that one was even in the running. How can you "tune" the
VM to handle bigger block sizes?


>>OK, I would like to see them. And also discussions of things like why
>>we shouldn't increase PAGE_SIZE instead.
> 
> 
> Because 4k is a good page size that is bound to the binary format? Frankly 
> there is no point in having my text files in large page sizes. However, 
> when I read a dvd then I may want to transfer 64k chunks or when use my 
> flash drive I may want to transfer 128k chunks. And yes if a scientific 
> application needs to do data dump then it should be able to use very high 
> page sizes (megabytes, gigabytes) to be able to continue its work while 
> the huge dumps runs at full I/O speed ...

So block size > page cache size... also, you should obviously be using
hardware that is tuned to work well with 4K pages, because surely there
is lots of that around.

-- 
SUSE Labs, Novell Inc.
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