az_pmem_reserve_pages error when starting Zing

What to do if Zing fails on startup with an error message like this:

ERROR: az_pmem_reserve_pages (num2mPages 193811)
Fatal error: os::safeSystem: command '/usr/sbin/zing-llpmem --reserve --partition 0 --pages 193811 --nodemask 0xFFFFFFFF' failed.
zing-memory: ERROR: Configure pmem failed
Fatal error: os::safeSystem: command '/etc/init.d/zing-memory restart' failed.

The most likely cause of this error is that there is not enough free RAM on the system, specifically, there are not enough free large pages (2MB or 4MB) for Zing to start up. This might be due to memory fragmentation. 

Since Zing ZST 5.21.7 an optional configuration is available to resolve this situation. Please consider upgrading the Zing ZST component, available for download on https://www.azul.com/software-downloads-and-documents/ and if needed, enable the additional configuration as described on the following page: https://docs.azul.com/zing/ZingAppA_EnhancedLinuxMemoryDefragmentation.htm

Since ZVM 19.07 Zing can also be installed and used without ZST. In that mode it does not need large pages and uses standard 4k Linux pages instead and won't be affected by memory fragmentation.

On older ZST versions the fastest way to try to fix this is to reboot your machine.