2. PERFORMANCE REPORTING ANALYSIS › 2.5 Virtual Storage Management Analysis › 2.5.4 Virtual Storage Concepts in MVS/XA › 2.5.4.4 Virtual Storage Subpools
2.5.4.4 Virtual Storage Subpools
Virtual storage is subdivided into different areas, which are
shown in Figure 2-175. Within these areas, virtual storage is
further subdivided into categories called subpools.
GETMAIN/FREEMAIN processing of the VSM will accept requests
for the subpool numbers shown in the Figure 2-176. The VSM
maps these requests into its own somewhat smaller group of
subpool numbers and allocates sufficient virtual address
space, in increments of 4KB pages, to satisfy any particular
GETMAIN request. The VSM will allocate virtual memory within
an area either from the bottom upward, or from the top
downward, depending upon the subpool involved. Storage
allocated in these subpools may be page fixed or pageable,
and fetch protected or not fetch protected. All these
characteristics are summarized for the various subpools in
the Figure 2-176.
+---------+-------+-----+------+---------------+------------+--------+---------+
|Requested|VSM |Page |Fetch |Type of Storage|Owner |Subpool |Automatic|
|Subpool |Subpool|Fixed|Pro- |And Allocation | |FREEMAIN|Freeing |
| | | |tected|Direction | | | |
+=========+=======+=====+======+===============+============+========+=========+
| 000-127 |000-127| No | Yes |PVT/EPVT/Up |Current Task| Yes | Task |
| 226 | 226 | Yes | No |SQA/Down |None | No | No |
| 227 | 227 | Yes | Yes |CSA/ECSA/Down |None | No | No |
| 228 | 228 | Yes | No |CSA/ECSA/Down |None | No | No |
| 229 | 229 | No | Yes |PVT/EPVT/Down |Current Task| Yes | Task |
| 230 | 230 | No | No |PVT/EPVT/Down |Current Task| Yes | Task |
| 231 | 231 | No | Yes |CSA/ECSA/Down |None | No | No |
| 233 | 255 | Yes | No |LSQA/ELSQA/Down|Current Task| Yes | Task |
| 234 | 255 | Yes | No |LSQA/ELSQA/Down|Jobstep Task| No | Jobstep |
| 235 | 255 | Yes | No |LSQA/ELSQA/Down|Memory | No | No |
| 236 | 236 | No | No |PVT/SWA/Down |Current Task| Yes | Task |
| 237 | 237 | No | No |PVT/SWA/Down |Current Task| Yes | Task |
| 239 | 239 | Yes | Yes |SQA/ESQA/Down |None | No | No |
| 240 | 000 | No | Yes |PVT/EPVT/Up |Current Task| Yes | Jobstep |
| 241 | 241 | No | No |CSA/ECSA/Down |None | No | No |
| 245 | 245 | Yes | No |SQA/ESQA/Down |None | No | No |
| 250 | 000 | No | Yes |PVT/EPVT/Up |Current Task| Yes | Jobstep |
| 251 | 251 | No | Yes |PVT/EPVT/Up |Jobstep Task| Yes | Jobstep |
| 252 | 252 | No | No |PVT/EPVT/Up |Jobstep Task| Yes | Jobstep |
| 253 | 255 | Yes | No |LSQA/ELSQA/Down|Current Task| Yes | Task |
| 254 | 255 | Yes | No |LSQA/ELSQA/Down|Jobstep Task| No | jobstep |
| 255 | 255 | Yes | No |LSQA/ELSQA/Down|Memory | No | No |
+---------+-------+-----+------+---------------+------------+--------+---------+
Figure 2-176. Virtual Storage Subpool Characteristics
PVT/EPVT/SWA - PRIVATE AREA, EXTENDED PRIVATE AREA, AND
SCHEDULER WORK AREA
Subpool 240 has been retained for compatibility with MFT and
OS/VS1. This subpool and subpool 250 are translated by VSM
into GETMAINs for subpool 0. Requests for subpool 0 by tasks
running with storage protection key 0 in supervisor state are
translated to subpool 252. Any subpool in a user region will
be given the storage protection key of the task that issued
the first GETMAIN for that subpool. That task is considered
the owner of that subpool and all other requests for that
subpool will be given the same storage protection key.
Authorized region subpools consist of the Authorized User Key
subpools (AUK), 229 and 230, and the Scheduler Work Area
subpools (SWA), 236 and 237. The AUK supports multiple
storage protection keys, whereas the entire SWA is assigned
storage protection keys of 1.
LSQA/ELSQA - LOCAL SYSTEM QUEUE AREA AND EXTENDED LOCAL
SYSTEM QUEUE AREA
VSM defines subpools 233, 234, and 235 to be equivalent to
253, 254, and 255, respectively. Internally, all are managed
as subpool 255. All will have a storage protection key of 0.
CSA/ECSA - COMMON SYSTEM AREA AND EXTENDED COMMON SYSTEM AREA
Subpools 227, 228, 231, and 241 give every possible
combination of page fixing and fetch protection. In order to
help ensure data and program integrity, VSM supports multiple
storage protection keys for the CSA.
SQA/ESQA - SYSTEM QUEUE AREA AND EXTENDED SYSTEM QUEUE AREA
All virtual storage assigned to SQA which is not currently
allocated to subpools 226 or 239 is considered to be part of
subpool 245. All these SQA subpools are assigned a storage
protection key of 0.
Note that subpool 226 is never allocated above the 16MB
boundary line.