Joni,
> I have a TSM server on the os/390 at version 5.2.2.5 and I was wondering if
> what you see below could cause my logs to fill up and cause performance
> issues? I always thought that MaxQuickFree should be greater than Freeheld
> bytes, but how do I actually fix this? Thanks in advance!
>
> MAX initial storage 536870912 (512.0 MB)
> Freeheld bytes 11436776 (10.9 MB)
> MaxQuickFree bytes 10737418 (10.2 MB)
> 307 Page buffers of 13107 : 418 buffers of 1638.
> 8 Large buffers of 819 : 77 XLarge buffers of 102.
> 14 buffers free: 336690 hiAlloc buffers: 106165 current buffers.
> 100554 units of 104 bytes hiAlloc: 89786 units of 104 bytes hiCur.
According to my understanding of Freeheld and MaxQuickFree, the above
numbers indicate a definite, and fixable, performance problem. As I
understand things:
At startup on MVS, MaxQuickFree is set at 2% of the region size. This
pool used to satisfy 'small' storage requests; a chunk of storage is
getmained, but not freemained - it becomes part of Freeheld and can be
used again without getmaining. Things are fine until the size of Freeheld
equals or exceeds MaxQuickFree; at that point, and forever after, these
'small' storage requests result in getmain/freemain, and that's when
performance goes down the tube...I call it the 'getmain/freemain frenzy'.
If you can get MaxQuickFree big enough (see next paragraph), you
*shouldn't* run into this problem.
You can indirectly increase MaxQuickFree (up to a point) by increasing the
region size. But there is also the secret/magic (i.e., undocumented)
'show memu set maxquick' command, which can be used to arbitrarily set the
size of MaxQuickFree. For example, 'show memu set maxquick 83886080' sets
MaxQuickFree to 80 MB.
I was seeing abysmal performance on a z/OS server after it had been up for
a while and Freeheld exceeded MaxQuickFree. I set up an admin schedule to
set MaxQuickFree to 80 MB and had the schedule run every hour (just so
that it would run within the first hour after startup). I never saw the
problem again; Freeheld usually peaked out somewhere around 25 MB for me.
Hope this helps,
Bill
Bill Kelly
Auburn University OIT
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