SERVGA parameter
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.
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:
| Bit | Server table placed above the bar |
|---|---|
X'02000000' | FTBL |
X'00800000' | GTBL — requires version 7.5 or later of Model 204. |
X'00004000' | NTBL — requires version 7.5 or later of Model 204. |
X'00002000' | QTBL — requires version 7.5 or later of Model 204. |
X'01000000' | XTBL — requires version 7.6 or later of Model 204. |
X'00400000' | ITBL — requires version 7.6 or later of Model 204. |
X'00100000' | FSCB — requires version 7.6 or later of Model 204. |
X'00080000' | STBL — requires version 7.6 or later of Model 204. |
X'00040000' | VTBL — requires version 7.6 or later of Model 204. |
X'00020000' | TTBL — requires version 7.6 or later of Model 204. |
X'00010000' | HTBFRS — requires version 7.6 or later of Model 204. |
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.
The above mentioned tables can alternatively be placed above-the-bar in a non-swappable area. This can be indicated with the SERVNSA and SERVNSSZ parameters. The bits corresponding to the tables should not be set in both SERVNSA and SERVGA — if they are, an error message will be issued and the online will fail to come up.
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.