SERVGA parameter

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Above the bar server areas

Summary

Default value
0
Parameter type
System
Where set
On User 0's parameter line
Related products
All
Introduced
Model 204 V7.5

Description

The SERVGA parameter controls which server tables are allocated in the ATB-swappable-server area.

In Model 204 version 7.5, only NTBL and QTBL can be placed above-the-bar in a swappable area.
Each server table to be allocated in that area is controlled by a bit in SERVGA. If the bit is on, the corresponding server table is allocated in the ATB-swappable-server area.

The bits are:

BitServer table placed above the barRequired version of Model 204
X'02000000'FTBL7.6 or later
X'01000000'XTBL7.6 or later
X'00800000'GTBL7.6 or later
X'00400000'ITBL7.6 or later
X'00200000'PDL7.9 or later
X'00100000'FSCB7.6 or later
X'00080000'STBL7.6 or later
X'00040000'VTBL7.6 or later
X'00020000'TTBL7.6 or later
X'00010000'HTBFRS7.6 or later
X'00004000'NTBL 7.5 or later
X'00002000'QTBL7.5 or later
X'00001000'Server-swap table7.9 or later


Note: These bits can also be set in SERVNSA but should not be set in both SERVGA and SERVNSA — if they are, an error message is issued and the Online fails to come up.

SERVGSZ is the amount of space in bytes required for the swappable above-the-bar server tables per server. The total amount of storage allocated for swappable above-the-bar server areas equals SERVGSZ rounded to 4K and multiplied by NSERVS. When sizing SERVGSZ, it should accomodate the largest swappable above-the-bar table sizes that might be needed.

Some server tables can alternatively be placed above-the-bar in a non-swappable area. This can be indicated with the SERVNSA and SERVNSSZ parameters. In Model 204 7.9 and later, if PDL is placed above-the-bar it is recommended that LPDLST be set to its maximum value of 65536.

While it might seem odd to have above-the-bar swappable server areas, especially if swapping to above-the-bar memory, placing NTBL and QTBL in a swappable area can save quite a bit of real memory. This is especially true if the RESPAGE parameter is set to a non-zero value and there are significantly more users (NUSERS) than servers (NSERVS). In such a case, most swapped out users would either be using a resident (shared) NTBL and QTBL, or they would be logged out and only using a single 4K page. As such, reserving the amount of space required for NTBL and QTBL (which can typically get quite large) in the non-swappable above-the-bar area for all the swapped out users can waste a significant amount of real storage.

See also