SERVGA parameter: Difference between revisions
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==Description== | ==Description== | ||
<p>The <var> | <p>The <var>SERVGA</var> parameter, along with the <var>SERVGSZ</var> parameter, control swappable server areas that are placed above the 2G bar.</p> | ||
Each server table to be allocated in the above-the-bar swappable area is controlled by a bit in <var>SERVGSA</var>; if the bit is on, the corresponding server table is allocated in the above-the-bar swappable area. | Each server table to be allocated in the above-the-bar swappable area is controlled by a bit in <var>SERVGSA</var>; if the bit is on, the corresponding server table is allocated in the above-the-bar swappable area. | ||
Revision as of 14:21, 22 September 2014
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, along with the SERVGSZ parameter, control swappable server areas that are placed above the 2G bar.
Each server table to be allocated in the above-the-bar swappable area is controlled by a bit in SERVGSA; if the bit is on, the corresponding server table is allocated in the above-the-bar swappable 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 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.