Subject: Re: RFC - how to balance Dirty+Writeback in the face of slow
	writeback.
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Andrew Morton <akpm@osdl.org>
Cc: Neil Brown <neilb@suse.de>, David Chinner <dgc@sgi.com>,
       linux-kernel@vger.kernel.org
In-Reply-To: <20060816231448.cc71fde7.akpm@osdl.org>
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	 <20060815230050.GB51703024@melbourne.sgi.com>
	 <17635.60378.733953.956807@cse.unsw.edu.au>
	 <20060816231448.cc71fde7.akpm@osdl.org>
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Date: Thu, 17 Aug 2006 08:36:19 -0400
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On Wed, 2006-08-16 at 23:14 -0700, Andrew Morton wrote:
> btw, one thing which afaik NFS _still_ doesn't do is to wake up processes
> which are stuck in blk_congestion_wait() when NFS has retired a bunch of
> writes.  It should do so, otherwise NFS write-intensive workloads might end
> up sleeping for too long.  I guess the amount of buffering and hysteresis
> we have in there has thus far prevented any problems from being observed.

Are we to understand it that you consider blk_congestion_wait() to be an
official API, and not just another block layer hack inside the VM?

'cos currently the only tools for waking up processes in
blk_congestion_wait() are the two routines:

   static void clear_queue_congested(request_queue_t *q, int rw)
and
   static void set_queue_congested(request_queue_t *q, int rw)

in block/ll_rw_blk.c. Hardly a model of well thought out code...

  Trond

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