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'00004000'	NTBL
X'00002000'	QTBL

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.

QTBL and NTBL 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 NTBL and QTBL 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.