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Date: Wed, 25 Mar 2009 23:13:37 -0400
From: Theodore Tso <tytso@mit.edu>
To: Neil Brown <neilb@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       David Rees <drees76@gmail.com>, Jesper Krogh <jesper@krogh.cc>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Linux 2.6.29
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On Thu, Mar 26, 2009 at 01:50:10PM +1100, Neil Brown wrote:
> I shouldn't be too hard to add some concept of total time to this.
> If we track the number of write-outs per unit time and use that together
> with a "target time for fsync" to scale the 'dirty_bytes' number, we
> might be able to auto-tune the amount of dirty space to fit the speeds
> of the drives.
> 
> We would probably start with each device having a very low "max dirty"
> number which would cause writeouts to start soon.  Once the device
> demonstrates that it can do n-per-second (or whatever) the VM would
> allow the "max dirty" number to drift upwards.  I'm not sure how best
> to get it to move downwards if the device slows down (or the kernel
> over-estimated).  Maybe it should regularly decay so that the device
> keeps have to "prove" itself.

This seems like a really cool idea.

						-Ted
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