CSA

CSA=(a,b) 

This parameter specifies the sizes of the virtual common service area (CSA) and extended CSA. The subparameter "a" specifies the size of the CSA, located below 16MB. The subparameter "b" specifies the size of the extended CSA, located above 16MB.

The specified size of the CSA is subtracted from the bottom of PLPA, after the bottom PLPA address is rounded down to the next 4KB (page) boundary. If the resulting virtual address for the bottom of the CSA is not on a megabyte boundary, further rounding down occurs so that the bottom CSA address is on the next megabyte boundary.

Similarly, the specified size of the extended CSA is added to the top of the extended PLPA, after the top extended PLPA address is rounded up to the next 4-KB boundary. If the resulting virtual address for the top of the extended CSA is not on a megabyte boundary, further rounding up occurs so that the top extended CSA address is on the next megabyte boundary.

The CSA (including the extended CSA) is an address range in each address space that is used for common system functions (functions not related to a particular address space). For example, the system allocates buffers for LOG and SMF from the CSA.

In selecting values for the CSA parameter, understand that the system's process of rounding to a 1MB boundary can cause up to 1MB of storage from the private area to be allocated to the CSA. However, consider the following:

• If the virtual storage manager runs out of SQA, it will try to obtain space from the CSA.
• A large CSA size will reserve space for future LPA growth. Such growth would be hampered if users were allowed to obtain very large private areas. A large CSA specification effectively limits the maximum private area that a user job can acquire.

If a shortage occurs in CSA, ECSA, SQA, or ESQA, you can use the storage tracking function to collect information about jobs or address spaces that own storage in those areas. With that information, you can identify jobs or address spaces that obtain an excessive amount of storage. If those jobs or address spaces have code to free the storage when they are canceled, you might relieve the shortage and avoid an IPL if you use an operator command to cancel those jobs or address spaces.

When you turn the storage tracking function on, you might experience a small performance degradation and an increase in ESQA usage. For more information about common storage tracking, including how to turn the function on or off, see DIAGxx (control common storage tracking and GFS trace).

Note: If you allocate excessive amounts of CSA or SQA, the system generates a warning message, and you must respecify the CSA parameter. The system also generates a warning message when the size of the entire common area below 16MB exceeds 8MB.

Value Range: Each a value can be expressed as:

• A decimal number, n, indicating n 1KB (1024-byte) blocks. The number is 0 through 9999.
• A decimal number followed by K, nK, indicating n 1KB blocks. The number is 0 through 9999.
• A decimal number followed by M, nM, indicating n 1MB (1024*1024-byte) blocks. The number is 0 through 9.

Each b value can be expressed follows. Note that the maximum values are accepted, but not recommended because they would result in a private region that is too small. Do not specify more than you think you might ever need.

• A decimal number, n, indicating n 1KB blocks. The number is 0 through 2080767.
• A decimal number followed by K, nK, indicating n 1KB blocks. The number is 0 through 2080767.
• A decimal number followed by M, nM, indicating n 1MB blocks. The number is 0 through 2031.

Default Range: For each subparameter, 100 through 1023KB (depending on the amount of storage added because of rounding to a segment boundary).

Associated Parmlib Member: Not applicable.