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

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Message-ID: <Pine.LNX.4.64.0704252341560.30340@schroedinger.engr.sgi.com>
Date:	Wed, 25 Apr 2007 23:46:06 -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:

> Yeah. IMO anti-fragmentation and defragmentation is the hack, and we
> should stay away from higher order allocations whenever possible.

Right and we need to create series of other approaches that we then label 
"non-hack" to replace it. 

> Hardware is built to handle many small pages efficintly, and I don't
> understand how it could be an SGI-only issue. Sure, you may have an
> order of magnitude or more memory than anyone else, but even my lowly
> desktop _already_ has orders of magnitude more pages than it has TLB
> entries or cache -- if a workload is cache-nice for me, it probably
> will be on a 1TB machine as well, and if it is bad for the 1TB machine,
> it is also bad on mine.

There have been numbers of people that have argued the same point. Just 
because we have developed a way of thinking to defend our traditional 4k 
values does not make them right.

> If this is instead an issue of io path or reclaim efficiency, then it
> would be really nice to see numbers... but I don't think making these
> fundamental paths more complex and slower is a nice way to fix it
> (larger PAGE_SIZE would be, though).

The code paths can stay the same. You can switch CONFIG_LARGE pages off
if you do not want it and it is as it was.

If you would have a look the patches: The code is significantly cleanup 
and easier to read.
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