Re: Linux 2.6.29 [LWN.net]

From:		Andrew Morton <akpm-AT-linux-foundation.org>
To:		Linus Torvalds <torvalds-AT-linux-foundation.org>
Subject:		Re: Linux 2.6.29
Date:		Thu, 26 Mar 2009 17:11:48 -0700
Message-ID:		<20090326171148.9bf8f1ec.akpm@linux-foundation.org>
Cc:		Theodore Tso <tytso-AT-mit.edu>, David Rees <drees76-AT-gmail.com>, Jesper Krogh <jesper-AT-krogh.cc>, Linux Kernel Mailing List <linux-kernel-AT-vger.kernel.org>
Archive-link:		Article, Thread

On Wed, 25 Mar 2009 16:23:08 -0700 (PDT) Linus Torvalds <torvalds@linux-foundation.org> wrote:

> 
> 
> On Wed, 25 Mar 2009, Theodore Tso wrote:
> > > 
> > > The problem being that unlike the ratio, there's no sane default value 
> > > that you can at least argue is not _entirely_ pointless.
> > 
> > Well, if the maximum time that someone wants to wait for an fsync() to
> > return is one second, and the RAID array can write 100MB/sec
> 
> How are you going to tell the kernel that the RAID array can write 
> 100MB/s?
> 
> The kernel has no idea.
> 

userspace can do it quite easily.  Run a self-tuning script after
installation and when the disk hardware changes significantly.

It is very disappointing that nobody appears to have attempted to do
_any_ sensible tuning of these controls in all this time - we just keep
thrashing around trying to pick better magic numbers in the base kernel. 

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

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