Re: [DATAPOINT] pre7-6 will not swap

[Benjamin Redelings I <bredelin@ucla.edu>]

> and I suspect that we mightactually make the vmscan.c test more eager to
> swap stuff out: my private source tree says
> 
>         /*
>          * Don't do any of the expensive stuff if
>          * we're not really interested in this zone.
>          */
>         if (z->free_pages > z->pages_high)
>                 goto out_unlock;
> 
> in vmscan.c, and that seems to be quite well-behaved too (but if somebody
> has the energy to test the two different versions, I'd absolutely love to
> hear results..)

Although I would have thought that putting this test in would have no
effect on performance, it actually kills performance.  Since the test
appears very reasonable, I think this means we have a bug elsewhere, and
that removing this reasonable test cures a symptom, but not the bug.

OK, details.
	With Linus's test, the kernel does not want to swap much.  It is a
little better than the pervious version of the test, but much lower than
if the test was removed.  One result is that the cache shrinks to low
sizes like 14Mb/64Mb, when there are several unused daemons that could 
be swapped out.	
	Also, the WRONG PROCESSES are swapped out.  Several large daemons that
were swapped out w/o the test, are now left in core.  Instead, RUNNING
programs are swapped out, like netscape.  Even worse, running xquake and
'tar -xf linux.tar' makes the system non-responsive - the VM continues
paging the quake ENGINE in and out and in and out :P
	It looks like some processes (my unused daemons) are scanned only once,
and then get stuck at the end of some list?  Is that a possible
explanation? <guessing> Perhaps Rik's moving list-head idea is needed?
</guessing>.

carry on,
-benRI
-- 
"I want to be in the light, as He is in the Light,
 I want to shine like the stars in the heavens." - DC Talk, "In the
Light"
Benjamin Redelings I      <><     http://www.bol.ucla.edu/~bredelin/
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