linux-kernel - Re: Change in default vm_dirty

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Message-ID: <alpine.LFD.0.98.0706201015370.3593@woody.linux-foundation.org>
Date:	Wed, 20 Jun 2007 10:17:40 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>, tim.c.chen@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: Change in default vm_dirty_ratio

On Wed, 20 Jun 2007, Peter Zijlstra wrote:
> 
> Building on the per BDI patches, how about integrating feedback from the
> full-ness of device queues. That is, when we are happily doing IO and we
> cannot possibly saturate the active devices (as measured by their queue
> never reaching 75%?) then we can safely increase the total dirty limit.

The really annoying things are the one-off things. You've been happily 
working for a while (never even being _close_ to saturatign any IO 
queues), and then you untar a large tree.

If the kernel now let's you dirty lots of memory, you'll have a very 
unpleasant experience.

And with hot-pluggable devices (which is where most of the throughput 
problems tend to be!), the "one-off" thing is not a "just after reboot" 
kind of situation.

So you'd have to be pretty smart about it.

		Linus
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