New P630 AIX 5.1 MU4 with slowly increasing mbuf paging space allocation

From: Michael Vraniak (mvraniak_at_yahoo.com)
Date: 10/30/03 

Date: 30 Oct 2003 13:33:59 -0800

We have recently installed two new P630 machines. They each have 4GB
of physical memory as well as 4GB of paging space. As soon as we start
applications that utilize the network we see paging space increase.
Using "svmon -S -g" we can see that memory is being allocated more and
more to mbufs. Yesterday our allocation was 1924088KB and today
1925524KB. Examining week long data we see an increase of about 10MB a
week in mbuf memory allocation.

The applications that we start are the same ones that we have been
using on AIX 4.3.3 ML10 servers without the same problem. They are a
Cache database with user interface via telnet and a monitoring utility
that exports system data to a central data repository via ssh copies.

A call to IBM confirmed that we are at the latest revs. They suggested
three things:
1) Change maxmbuf to lock in at a lower value (disable dynamic system
setting)
2) Switch from 64bit to 32bit OS
3) Increase the size of the swap space

I am hesitant to do #3 since, to me, this would just be masking the
issue and I also feel that #2 is a step back rather than a solution.

Has anyone experienced this issue?
What do you think of locking in maxmbuf rather than letting the system
dynamically set it?

Thanks in advance,

Michael Vraniak
mvraniak@yahoo.com

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