Re: Why active list and inactive list?

[Howard Chu <hyc@symas.com>]

Peter Zijlstra <a.p.zijls...@chello.nl> said:
> I'm still torn between CLOCK-Pro and CART. 
>
> CLOCK-Pro is still vulnerable to the cyclic scan use case, since at that
> time all pages will have equal distance.

I was recently testing CLOCK-Pro for the entry cache in OpenLDAP, with this 
cyclic scan case. I've set it aside for now, but if anyone is interested in 
playing with a user-level version as opposed to these kernel adaptations, an 
early version of mine is at
http://www.openldap.org/its/index.cgi/Software%20Enhancements?id=4807

I found that although it managed to allow some cached pages to be reused, it 
also forced several full sweeps of the clock in each scan. Overall it 
performed more slowly than regular CLOCK due to these extra sweeps. (In our 
case, moving the hands required some expensive lock manipulation. Possibly if 
I found a better locking strategy there the performance cost would come down.)

--
  -- Howard Chu
  Chief Architect, Symas Corp.  http://www.symas.com
  Director, Highland Sun        http://highlandsun.com/hyc
  OpenLDAP Core Team            http://www.openldap.org/project/
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