Re: VM Requirement Document - v0.0

[Martin Knoblauch <Martin.Knoblauch@TeraPort.de>]

>> * 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. 

Rik> ... but I fail to see this one. If we get a low cache hit rate, 
Rik> couldn't that just mean we allocated too little memory for the 
Rik> cache ? 

 maybe more specific: If the hit-rate is low and the cache is already
70+% of the systems memory, the chances maybe slim that more cache is
going to improve the hit-rate. 

 I do not care much whether the cache is using 99% of the systems memory
or 50%. As long as there is free memory, using it for cache is great. I
care a lot if the cache takes down interactivity, because it pushes out
processes that it thinks idle, but that I need in 5 seconds. The caches
pressure against processes should decrease with the (relative) size of
the cache. Especially in low hit-rate situations.

 OT: I asked the question before somewhere else. Are there interfaces to
the VM that expose the various cache sizes and, more important,
hit-rates to userland? I would love to see (or maybe help writing in my
free time) a tool to just visualize/analyze the efficiency of the VM
system.

Martin
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