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Date: Fri, 21 Dec 2007 23:32:36 -0800
From: David G Lawrence <dg@dglawrence.com>
To: Alfred Perlstein <alfred@freebsd.org>
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Cc: freebsd-net@freebsd.org, freebsd-stable@freebsd.org
Subject: Re: Packet loss every 30.999 seconds
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> > > Can you use a placeholder vnode as a place to restart the scan?
> > > you might have to mark it special so that other threads/things
> > > (getnewvnode()?) don't molest it, but it can provide for a convenient
> > > restart point.
> > 
> >    That was one of the solutions that I considered and rejected since it
> > would significantly increase the overhead of the loop.
> >    The solution provided by Kostik Belousov that uses uio_yield looks like
> > a find solution. I intend to try it out on some servers RSN.
> 
> Out of curiosity's sake, why would it make the loop slower?  one
> would only add the placeholder when yielding, not for every iteration.

   Actually, I misread your suggestion and was thinking marker flag,
rather than placeholder vnode. Sorry about that. The current code
actually already uses a marker vnode. It is hidden and obfuscated in
the MNT_VNODE_FOREACH macro, further hidden in the __mnt_vnode_first/next
functions, so it should be safe from vnode reclaimation/free problems.

-DG

David G. Lawrence
President
Download Technologies, Inc. - http://www.downloadtech.com - (866) 399 8500
The FreeBSD Project - http://www.freebsd.org
Pave the road of life with opportunities.