Re: VM Requirement Document - v0.0

[Jason McMullan]

On Tue, Jun 26, 2001 at 06:21:21PM -0300, Rik van Riel wrote:
> > 	* If we're getting low cache hit rates, don't flush
> > 	  processes to swap.
> > 	* If we're getting good cache hit rates, flush old, idle
> > 	  processes to swap.
> 
> ... but I fail to see this one. If we get a low cache hit
> rate, couldn't that just mean we allocated too little memory
> for the cache ?

	Hmmm. I didn't take that into consideration. But at the
same time, shouldn't a VM be able to determine that its cache
strategy is causing _more_ (absolute) misses by increasing it 
cache size? The percentage of misses may go down, but total 
device I/O may stay the same.

	So let's see... I'll rephrase that 'Motiviation' as:

	* Minimize the total medium/slow I/Os that occur over a 
	  sliding window of time. 

	Is that a more general case?
 
> Also, how would we translate all these requirements into
> VM strategies ?

	First, I would like to translate them into measurements.
Once we know how to measure these criteria, its possible to
formalize the feedback mechanism/accounting that a VM should
be aware of.

	In the end, I would like a VM to have some idea of
how well its performing, and be able to attempt various
well-known strategies based upon its own performance.

-- 
Jason McMullan, Senior Linux Consultant
Linuxcare, Inc. 412.432.6457 tel, 412.656.3519 cell
[e-mail], http://www.linuxcare.com/
Linuxcare. Putting open source to work.