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Date: Mon, 29 Aug 2005 20:36:41 -0700 (PDT)
From: Don Lewis <truckman@FreeBSD.org>
To: jd@ugcs.caltech.edu
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Cc: mckusick@mckusick.com, freebsd-stable@FreeBSD.org, mkb@incubus.de,
	markir@paradise.net.nz
Subject: Re: Sysinstall automatic filesystem size generation.
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On 29 Aug, Jon Dama wrote:

> It seems you need to add a layer of indirection.  (owing to biodone being
> called merely when the drive has cached the request).  What you know is
> that those operations marked completed by biodone are in fact done only
> after a (costly) flush cache operation is executed.
> 
> Therefore you want to delay this operation for as long as possible, in
> fact until you actually depend on biodone being honest.  I.e., at the time
> another operation is inserted into the WORKLIST.
> 
> The secret I think is to keep track of which bp's marked B_DONE by
> biodone that have been certified by a flush cache.  Thus permitting you to
> avoid some cache flushes.  Furthermore, the softdep code has to be
> responsible for envoking the flush cache operation when it notices that
> the B_DONE flag that it cares about does not have a matching
> B_REALLY_DONE flag, which every block should have that had B_DONE set
> before the flush cache operation happened.

I believe you are correct.