Re: Prezeroing V2 [0/3]: Why and When it works

[Linus Torvalds]

On Fri, 24 Dec 2004, Arjan van de Ven wrote:
> 
> problem is.. will it buy you anything if you use the page again
> anyway... since such pages will be cold cached now. So for sure some of
> it is only shifting latency from kernel side to userspace side, but
> readprofile doesn't measure the later so it *looks* better...

Absolutely. I would want to see some real benchmarks before we do this.  
Not just some microbenchmark of "how many page faults can we take without
_using_ the page at all".

I agree 100% with you that we shouldn't shift the costs around. Having a
hice hot-spot that we know about is a good thing, and it means that
performance profiles show what the time is really spent on. Often getting
rid of the hotspot just smears out the work over a wider area, making
other optimizations (like trying to make the memory footprint _smaller_
and removing the work entirely that way) totally impossible because now
the performance profile just has a constant background noise and you can't 
tell what the real problem is.

		Linus
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