Re: Delaying writes to disk when there's no need

[Nick Piggin <piggin@cyberone.com.au>]

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".