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: <20060817081415.f48fbb37.akpm@osdl.org>
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Date: Thu, 17 Aug 2006 12:22:59 -0400
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On Thu, 2006-08-17 at 08:14 -0700, Andrew Morton wrote:
> Take a look at blk_congestion_wait().  It doesn't know about request
> queues.  We'd need a new
> 
> void writeback_congestion_end(int rw)
> {
> 	wake_up(congestion_wqh[rw]);
> }
> 
> or similar.

...and how often do you want us to call this? NFS doesn't know much
about request queues either: it writes out pages on a per-RPC call
basis. In the worst case that could mean waking up the VM every time we
write out a single page.

Cheers,
  Trond

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