Look at past SHARE presentations on the subject as well the Redbooks.
They carry a wealth of information related to Linux guests and paging.
Jim
On 2/23/2010 12:23 PM, Mike Walter wrote:
Mark,
Yes, we're paging. A lot! And the page volumes are filling up too!
Not being a performance geek, and without any knowledge of your
environment other except that you have Linux for System z guests,
something sounds a little fishy.
Just guessing from other's past posts: could it be that your Linux guests
had been given VM sizes based on what the distributed servers had?
IIRC, Linux caches a lot of files in its storage. That's great in a
distributed server that has lower I/O throughput (all I/O is serviced by
the CPU on the motherboard vs. being handed off to an I/O processor on
System z), and where distributed memory is a lot cheaper than System z
memory.
On System z, memory is (relatively) expensive, I/O's are VERY fast (and do
not impact the CPU much), and MDISK cache is quite good. Giving Linux for
System z servers lots of memory because that's what they had on
distributed servers (presuming that the memory is mostly file caching),
and having the Linux server also cached in minidisk cache is quite a waste
(double caching). IIRC, MDCACHE beats Linux cache in almost every case.
If you have a good performance monitor for your Linux guests, try to see
*why* they need so much memory. If it's file cache, try reducing the vm
size significantly (IIRC, Jim Vincent used to recommend 2G or less for
Websphere servers).
Getting the Linux guest memory requirements reduced could improve your
z/VM paging requirements.
Good hunting!
Mike Walter
Hewitt Associates
The opinions expressed herein are mine alone, not my employer's.
