On 08/22/2016 07:42 AM, Jaco Kruger wrote:
> Good day,
>
> We are preparing to migrate from z/OS 1.13 to z/OS 2.2. The TST LPAR has 8GB
> Central Storage assigned and it resides on IBM z13.
>
> On z/OS 1.13, the UIC count is 65535 during and after the IPL. On z/OS 2.2,
> the UIC count is below 1000 during the IPL and it gradually increases.
>
> The Central Storage have been increased to 50GB on the TST LPAR, but the UIC
> count during the IPL stays below 1000, even when only basic components are
> started. There is no PAGING to Auxiliary storage.
>
> HVCOMMON, HVSHARE are DEFAULT values. LFAREA is set to 0M
>
> The WSET and Memory Object sizes (as obtained from RMF) have been compared
> between z/OS 1.13 and z/OS 2.2 and there are no candidates that justifies the
> low UIC count.
>
> Any idea on how to determine the reason for the low UIC count ?
>
> Regards
>
> Jaco Kruger
>
>
It sounds like z/OS 1.13 was setting UIC of pages referenced during the
IPL at unsigned-halfword high-values, which is really counter to the
definition of UIC (seconds since page last referenced), and that z/OS
2.2 is more properly initializing UIC of IPL-related pages to zero,
which would mean no page's UIC could possibly exceed 1000 until 1000
seconds (16.7 minutes) after the IPL. Perhaps initialization with
high-values was an earlier convention to insure that physical pages
which possibly had one-time use during the IPL process would always be
the first to be reclaimed when production address spaces began to run
and the available frame count became low, but I would suspect this could
also force more LPA pages to be paged out that might subsequently have
to be paged back in once production workloads were fully active.
I would guess that with the much larger physical memory sizes in use
today, any shortages of free pages occurs enough later after the IPL for
normal page UIC value conventions to be sufficient to differentiate
what pages are inactive without special logic to give unique treatment
to pages touched during the IPL. That you are seeing a lack of any
paging would seem to support this hypothesis, and that the low UIC seen
with z/OS 2.2 is actually a fix, not a problem.
Joel C. Ewing
--
Joel C. Ewing, Bentonville, AR [email protected]
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