linux-kernel - Re: Linux 2.6.29

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Message-ID: <alpine.LFD.2.00.0903261723250.3994@localhost.localdomain>
Date:	Thu, 26 Mar 2009 17:27:43 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Theodore Tso <tytso@....edu>, David Rees <drees76@...il.com>,
	Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

On Thu, 26 Mar 2009, Andrew Morton wrote:
> 
> userspace can do it quite easily.  Run a self-tuning script after
> installation and when the disk hardware changes significantly.

Uhhuh.

"user space can do it".

That's the global cop-out.

The fact is, user-space isn't doing it, and never has done anything even 
_remotely_ like it. 

In fact, I claim that it's impossible to do. If you give me a number for 
the throughput of your harddisk, I will laugh in your face and call you a 
moron.

Why? Because no such number exists. It depends on the access patterns. If 
you write one large file, the number will be very different (and not just 
by a few percent) from the numbers of you writing thousands of small 
files, or re-writing a large database in random order.

So no. User space CAN NOT DO IT, and the fact that you even claim 
something like that shows a distinct lack of thought.

> Maybe we should set the tunables to 99.9% to make it suck enough to
> motivate someone.

The only times tunables have worked for us is when they auto-tune. 

IOW, we don't have "use 35% of memory for buffer cache" tunables, we just 
dynamically auto-tune memory use. And no, we don't expect user space to 
run some "tuning program for their load" either.

		Linus
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