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From: John Bradford <john@grabjohn.com>
Message-Id: <200303312251.h2VMp8gv000270@81-2-122-30.bradfords.org.uk>
Subject: Re: Delaying writes to disk when there's no need
To: piggin@cyberone.com.au (Nick Piggin)
Date: Mon, 31 Mar 2003 23:51:08 +0100 (BST)
Cc: cfriesen@nortelnetworks.com, helgehaf@aitel.hist.no, erik@hensema.net,
       linux-kernel@vger.kernel.org
In-Reply-To: <3E88C29A.7050308@cyberone.com.au> from "Nick Piggin" at Apr 01, 2003 08:35:06 AM
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> If the memory does get written to again before the writeout timeout
> then yeah its used some cpu, memory, pci, etc that it didn't have
> to.

It will presumably also have filled the cache with the writeout data.

> > Ultimately its all a tradeoff.  Do you write now, or do you hold off 
> > and hope that you can throw away some of the writes because new stuff 
> > will home in to overwrite them?
> 
> Yes it is a tradeoff. Having an idle disk gives more weight to "write now".

Not necessarily.  What if you are using a solid state disk which only
allows a relatively low number of re-write cycles?  What if the disk
is spun down, and spinning it up uses a lot of power?  On a laptop,
you don't necessarily want the disk spinning up just to write one
sector.

John.
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