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Date: Tue, 01 Apr 2003 08:58:32 +1000
From: Nick Piggin <piggin@cyberone.com.au>
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To: John Bradford <john@grabjohn.com>
CC: cfriesen@nortelnetworks.com, helgehaf@aitel.hist.no, erik@hensema.net,
       linux-kernel@vger.kernel.org
Subject: Re: Delaying writes to disk when there's no need
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John Bradford wrote:

>>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.
>
What cache?

>
>
>>>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.
>
Yes it does. The factors you mention just add (a lot) more
weight to "hold off".

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