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Date:      Fri, 10 Nov 2000 00:12:36 +0100 (CET)
From:      Marius Bendiksen <mbendiks@eunet.no>
To:        Poul-Henning Kamp <phk@freebsd.org>
Cc:        arch@freebsd.org
Subject:   Re: Green/Yellow/Red state for the VM system.
Message-ID:  <Pine.BSF.4.05.10011100007420.25048-100000@login-1.eunet.no>
In-Reply-To: <28041.973635706@critter>

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Sounds good to me, but I have a small alteration to suggest. You might
want to introduce the color ORANGE, instead of yellow, and have
yellow and green be per-subsystem states, and orange and red be global,
so as to be able to adapt more gradually to the impending highwatermark.

Also, I'd suggest going through with the idea of posting signals to user
processes before hitting a real high water mark, preferrably also color
coded, as opposed to SIGDANGER, which I don't see as much use in. The use
of color, however, when extended into userland, allows software doing
clustering and such to signal that the other hosts in the cluster should
cover for it, and that it does not want any more load. The use of a black
or green signal (depending on granularity) to say "act normal" prevents
severe DoS attacks, I think.

---
Marius Bendiksen




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