Re: [ck] Re: [PATCH][RFC] vm: swap prefetch

[Pedro Venda]

On Friday 02 September 2005 14:10, Con Kolivas wrote:
> Yes that about wraps up what it does. It would be even better used in a
> real world situation on a machine that has trouble "getting started" after
> an overnight updatedb run and has been idle for a while.

thanks. your last comment about updatedb reminds me of my "server"'s kind of 
load :-p

> > about the Hans's proposal - it would increase power consumption, because
> > of increased disk activity. about con's swap prefetch, I'm not so sure...
>
> Depends entirely on workload. Overall I think this increases power
> consumption because the disk does tiny little reads and keeps spinning
> until it has finished prefetching as much as it can. I was thinking it
> could be made configurable and to detect when laptop mode was enabled and
> so on... if it is thought that this is desirable of course.

Not counting hard drive spin-down or even standby, I find no reason for 
increased power consumption on swap prefetch mechanism, except for page 
syncing (swap&mem) and perhaps upon process killing...

Question: Imagine some big app like firefox completely swapped. killing it 
implies swapping out the process memory entirely to free allocated pages?

- If it does, then your swap prefetch may not increase power consumption by a 
measurable margin, because some of that swapped information was prefetched.
- If it does not, than prefetched swapped pages could be useless if the 
applications dies.

I don't know enough about the kernel VM to answer this on my own.

regards,
pedro venda.
-- 

Pedro João Lopes Venda
email: pjvenda < at > arrakis.dhis.org
http://arrakis.dhis.org

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