Redhat 7.3 kernel 2.4.20 bigmem kscand problems

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To: <redhat-list@redhat.com>
Date: Mon, 21 Jul 2003 15:00:18 +0100

We are running postgresql databases on dell poweredge
6650 servers with 12 GB of memory. They are running
Redhat 7.3, and we recently upgraded (as part of the
redhat updates) the kernel from 2.4.18-27.7.xbigmem
to 2.4.20-18.7bigmem.

Since updating to 2.4.20, we have had severe load
problems when the server gets busy. The busiest
process is usually kscand, and overall kscand and
kswapd have the highest CPU utilization times.

A recent test showed the servers to perform well
after initial boot, up until the cache memory filled
up (ie: almost no free memory left, applications
using only about 0.5 GB, and cached mem using about
11.5 GB). After that kscand gets much busier and
as the database use increases, load seems to escalate
wildly.

There appears to have been a change in the way VM is
handled between kernel 2.4.18 and 2.4.20. Is there
any documentation on this anywhere (we can't find any
yet) and has anyone else had any problems running
2.4.20 on large memory systems?

Is 2.4.20 recommended over 2.4.18 ? Any info or
practical experiences would be much appreciated.

Regards,
Chris.

-- 
Chris Miles
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