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

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Message-Id: <20070406040035.2f1e1105.akpm@linux-foundation.org>
Date:	Fri, 6 Apr 2007 04:00:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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 Fri, 06 Apr 2007 09:01:57 +0200 Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> 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

Yup, silly man thought that "congestion_wait" has something to do with
congestion ;)  I think it sort-of used to, once.

Now it really means no more than "block until a batch of writes complete".
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