crash in VMM when free < minfree?

From: Cameron Kaiser (ckaiser_at_floodgap.com)
Date: 08/31/05 

Date: 31 Aug 2005 08:04:05 -0500

I'm trying to tune up an old AIX 4.1.5 system we still have in service that
cannot be upgraded to a later version of AIX that has started crashing after
large backup jobs.

Watching the system with vmstat shows that after fre gets under minfree a
couple times (eight seems to be the average), the system will hang up.
lsps just before the predicted crash doesn't show much in use, and avm
in vmstat is baseline for this system, so it's not running out of paging
space.

I tried diminishing minperm to hang onto fewer file pages, and this didn't
make a difference. Right now, it hobbles along because I set maxfree so high
that as soon as fre gets under minfree, it frees up a stupid high number of
file pages and so it hits the minfree limit much less. This and a couple
scheduled reboots are holding it together, but there has to be a better way.

No changes to schedtune, btw.

Is there a bug in VMM in this kernel version that the box is triggering? 

--
      Cameron Kaiser * ckaiser@floodgap.com * posting with a Commodore 128
                personal page: http://www.armory.com/%7Espectre/
  ** Computer Workshops: games, productivity software and more for C64/128! **
                  ** http://www.armory.com/%7Espectre/cwi/ **

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