linux-kernel - Re: [PATCH 12/12] mm: per BDI congestion feedback

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Date:	Fri, 06 Apr 2007 09:01:57 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	miklos@...redi.hu, neilb@...e.de, dgc@....com,
	tomoki.sekiyama.qu@...achi.com, nikita@...sterfs.com
Subject: Re: [PATCH 12/12] mm: per BDI congestion feedback

On Thu, 2007-04-05 at 16:24 -0700, Andrew Morton wrote:
> On Thu, 05 Apr 2007 19:42:21 +0200
> root@...gramming.kicks-ass.net wrote:
> 
> > Now that we have per BDI dirty throttling is makes sense to also have oer BDI
> > congestion feedback; why wait on another device if the current one is not
> > congested.
> 
> Similar comments apply.  congestion_wait() should be called
> throttle_at_a_rate_proportional_to_the_speed_of_presently_uncongested_queues().
> 
> If a process is throttled in the page allocator waiting for pages to become
> reclaimable, that process absolutely does not care whether those pages were
> previously dirty against /dev/sda or against /dev/sdb.  It wants to be woken
> up for writeout completion against any queue.

OK, so you disagree with Miklos' 2nd point here:
  http://lkml.org/lkml/2007/4/4/137

And in the light of clear_bdi_congestion() being called for each
writeout completion under the threshold this does make sense.

So this whole 8-12/12 series is not needed and just served as an
learning experience :-/


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