These were a left over from when the private memory pools were
converted to use uma zones. The limit of UMA zones, however,
works differently. When a zone is limited to only one or two pages
than, on multi-cpu systems, processes can get stuck on the zonelimit,
because all remaining free items are in caches of other CPUs.
Also add rudimentary error handling in some places (panic) when a zone
cannot be created.
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