Host Logical Storage

The system execution area contains the CP nucleus, the prefix pages, dynamically allocated free storage and other CP-use pages, aliases (references to guest pages), and routines loaded with the CPXLOAD system configuration statement or the CP CPXLOAD command. The system execution area resides below 2 GB; its size depends on the real storage size. The system execution space page management table and the system frame table reside above 2 GB. To display the host logical storage address ranges that are in use or usable by the system for the system execution space, issue the CP QUERY SXSSTORAGE command.

Host logical storage addresses in the CP nucleus and the prefix pages are identity mapped to real storage (that is, the host logical storage addresses and host real storage addresses are identical). The rest of the system execution area is dynamic (not identity mapped). Host logical storage pages must be backed with frames in real storage before they can be used, but backing frames are not necessarily contiguous. Frames below 2 GB are used only when required, freeing CP to exploit backing frames above 2 GB for most operations. To check the status of pages in the system execution area, issue the CP QUERY SXSPAGES command. This command displays information such as the number of pages that are available or in use; the number of pages that are backed below 2 GB, above 2 GB, or unbacked; and the number of pages that are locked or reserved.

For descriptions of QUERY SXSSTORAGE and QUERY SXSPAGES, see z/VM: CP Commands and Utilities Reference.