Subject: Re: Change in default vm_dirty_ratio
From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Jones <davej@redhat.com>, tim.c.chen@linux.intel.com,
       linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>
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Date: Wed, 20 Jun 2007 10:35:36 +0200
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On Tue, 2007-06-19 at 21:44 -0700, Andrew Morton wrote:

> Anyway, this is all arse-about.  What is the design?  What algorithms
> do we need to implement to do this successfully?  Answer me that, then
> we can decide upon these implementation details.

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.

OTOH, when even with the per BDI dirty limit the device queue is
constantly saturated (contended) we ought to lower the total dirty
limit.

Lots of detail here to work out, but does this sound workable?

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