Re: VM Requirement Document - v0.0

From: Jason McMullan (
Date: Tue Jun 26 2001 - 16:29:13 EST

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,
Linuxcare. Putting open source to work.
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This archive was generated by hypermail 2b29 : Sat Jun 30 2001 - 21:00:15 EST