Description of DMDQPIN

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From Brian Thompson, IBM.

DMDQPIN is a utility to determine outstanding pages in vacating zones. The intended use is for problem determination when memory reclamation, aka dynamic memory downgrade, appears to have stopped making progress.

When dynamically removing memory from z/VM, you would start that process with the CP SET STORAGE command. This is an asynchronous command. You would want to issue CP QUERY STORAGE commands to determine the memory that has been reclaimed. There are scenarios where progress may stop due to pinned pages in the memory zones we are attempting to reclaim. The majority of these cases are the result of back level firmware.

This utility allows you to determine which pages and the virtual machines associated with them are pinned and stalling the downgrade. Various approaches can then be used to address the scenario. For more information on this, see the Memory Management Page.