linux-kernel - Re: A peek at the future of storage

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Date:	Wed, 12 Dec 2007 19:39:25 +0100
From:	Bernd Petrovitsch <bernd@...mix.at>
To:	Daniel Phillips <phillips@...nq.net>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-kernel@...r.kernel.org
Subject: Re: A peek at the future of storage

On Mit, 2007-12-12 at 10:02 -0800, Daniel Phillips wrote:
> On Wednesday 12 December 2007 09:46, J. Bruce Fields wrote:
[...]
> > People have proposed writing a daemon that just reads
> > /proc/net/rpc/nfsd periodically and uses that to adjust the number of
> > threads from userspace, probably subject to some limits in a config
> > file someplace. (Think that could do the job, or is there some reason
[...]
> So how would a userspace daemon know that kernel is blocking and new 
> threads are needed?  In kernel this is pretty easy: when a new request 
> arrives, look on the thread list and if none are available, generate a 
> new one.  Something special needs to be done to handle the case where 
> there are no threads available because they are all piled up on a 
> semaphore due to, for example, somebody unplugging the network cable 
> for a remote disk.  We have to avoid generating infinite threads in 
> that case.  Ideas?

Add a sysctl configurable maximum number of NFS threads and default it
to 8 (or whatever now the default value is).
And one wants probably some logic to kill them again if they are not
used long enough. And then you need/want another variable for the
minimum number of NFS threads around.

	Bernd
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