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To: Scott Long <scottl@freebsd.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Wed, 25 Aug 2004 15:45:12 MDT."
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Date: Thu, 26 Aug 2004 07:33:05 +0200
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cc: Matthew Jacob <mjacob44@yahoo.com>
cc: sos@freebsd.org
cc: arch@freebsd.org
Subject: Re: potential re change for 5.3? 
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In message <412D0868.9060203@freebsd.org>, Scott Long writes:

>I'm not suggesting anything different, just making a note of something
>that might be desirable in the future.  In a way, I see GEOM as having
>the potential to be like Netgraph where it intercepts operations that it
>wants to process through it's framework and lets ones that it doesn't 
>pass directly through without a decoupling through extra kernel threads.
>But that's only one possible strategy.  Introducing the concept of a
>I/O scheduler that spawns KSE's to handle individual I/O requests is
>another possibility.

Well, the problem here is that requests which cannot be dealt with
due to resource shortages should be queued at the level where they
require least resources.  A request queued inside a driver holds
far more resources than a request in the pure bio format at the
entrance to the driver for instance.

And spawning KSE's in low memory situations is a recipe for suicide.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.