Rik van Riel <[EMAIL PROTECTED]> wrote:
CLOCK-Pro is still vulnerable to the cyclic scan use case, since at that
time all pages will have equal distance.

That's fixable.  Just bias in favor of the already active
pages and only let pages with a clearly smaller interreference
distance replace them.

Yes, I asked Song Jiang about whether this was a normal behavior, and he mentioned it would be an easy fix.

Getting rid of swappiness is a very good thing, IMHO.
I have heard about a few customer workloads that required
changes to swappiness in order for the system to be able
to handle their workload at all.

Systems should not have to be tuned like that...

Can say that again...

The main problem I'm having is test cases, notably the lack thereof.
(and lack of time ofcourse ;-)

Yes, this is always a problem.  I am not aware of any complete
test cases to test page replacement.

"Complete" would seem to be impossible. Exercise all code paths, sure. But exercise all usage patterns, I think you're just going to have to pick a few scenarios and hope you didn't miss anything bad.

It would be easy to simulate some database by having part of
the dataset be the index and referencing that in an r^2 way,
and the rest being the data which is referenced less.  At that
point you can see how taking frequency into account helps.

However, tests like that are simply not complete.  They are
not representative of the things most people do with their
system.

Is *anything* really representative of "most people"? After all there is nobody out there who is actually Joe Average.

Something like AIM-7 suffers from the same problems...

Anybody?

No great ideas spring to mind. We very seldom run in machines that are memory-constrained, so very few of our tests are oriented toward that.

If you're just testing to see if getting rid of swappiness is feasible, I think a fair test would just be a program that alternately touches file-backed pages vs anonymous RAM. E.g., allocate 2GB of RAM and mmap 2GB of a file on a machine with only 2GB of free RAM. Walk through each memory range and make sure the balance of memory shifts as expected. Cycle that, increase the stride on each cycle, and toss some other variations in there. You don't need to drive real apps, you just need to have a couple of threads exerting pressure.
--
  -- 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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