Modify settings for managing the big page memory
Component: | BS2000 |
Functional area: | System control and optimization |
Domain: | SYSTEM-MANAGEMENT |
Privileges: | OPERATING |
Routing code: | R |
This command is rejected on /390 architecture (SUs /390 and S servers) with the message EMM2350.
Function
On SU x86, part of the main memory is made available as a big page memory for CISCFW compilation (1 big page is 4 Mbytes in size). When the system starts, BIG-PAGE-QUOTA in the MEMORY parameter set is used as a planned value for defining the percentage of the total main memory which is used as big page memory. The actual size of the big page memory is dependent on other factors, such as the possible number of logical machines (CPUs) and the minimum main memory.
The MODIFY-MEMORY-PARAMETERS command enables systems support to specify, while the system is operating, the management parameters of the big page memory from which the actual size of the big page memory is derived.
The following three management parameters can be modified using this command:
The percentage of main memory used for big pages (BIG-PAGE-QUOTA operand). This specification is a should-be value. When the value is modified the following must be taken into account:
An increase of this percentage can only lead to an increase of the big page memory during command execution if EXTEND-BIG-PAGES=*ON-QUOTA-DEFICIENCY is specified. Irrespective of the EXTEND-BIG-PAGES operand, increasing the percentage leads to an increase of the big page memory with a subsequent memory extension or increase of the minimum main memory under VM2000.
A reduction of this percentage can only lead to a reduction of the big page memory during command execution if REDUCE-BIG-PAGES=*ON-QUOTA-EXCESS is specified and unused big pages exist.
The specification of whether and in which situation big page memory can be reduced (REDUCE-BIG-PAGES operand). The following settings must be distinguished:
The big page memory may never be reduced.
The big page memory may only be reduced when there is a threat of core saturation.
The big page memory may only be reduced if its size exceeds the BIG-PAGE-QUOTA set. In this case big pages can be reduced within the command, in a subsequent command call with a lower percentage specification, or in the event of a memory reduction.
The settings “threatened core saturation” and “BIG-PAGE-QUOTA exceeded” can also be combined. Used big pages can also be requested back by CISCFW and then reduced.
The specification of whether and in which situation big page memory can be extended (EXTEND-BIG-PAGES operand). The following settings must be distinguished:
The big page memory may never be extended.
The big page memory may only be extended if there is an insufficient number of free big pages.
The big page memory may only be extended if its size is below the specified BIG-PAGE-QUOTA. In this case big pages can be extended within the command, in a subsequent command call with a higher percentage specification, or in the event of a memory extension.
The settings “insufficient number of free big pages” and “below BIG-PAGE-QUOTA” can also be combined. Used big pages can also be requested back by CISCFW and then reduced.
If big pages are reduced or extended during command execution, the message EMM2309 shows the new size of the big page memory.
Information on the configuration of the main memory, including the use of big pages, is provided by the SHOW-MEMORY-CONFIGURATION command.
Details of managing big pages are described in the context of main memory administration in the “Introduction to System Administration” [14].
Format
MODIFY-MEMORY-PARAMETERS |
BIG-PAGE-QUOTA = *UNCHANGED / <integer 0..99> ,REDUCE-BIG-PAGES = *UNCHANGED / *NO / list-poss(2): *ON-QUOTA-EXCESS / *ON-CORE-SATURATION ,EXTEND-BIG-PAGES= *UNCHANGED / *NO / list-poss(2): *ON-QUOTA-DEFICIENCY / *ON-BIG-PAGE-SATURATION |
Operands
BIG-PAGE-QUOTA = *UNCHANGED / <integer 0..99>
Specifies the percentage of main memory which is to be used for big pages.
BIG-PAGE-QUOTA = *UNCHANGED
The percentage defined at system startup using the MEMORY parameter or using a preceding MODIFY-MEMORY-PARAMETERS command is not modified.
BIG-PAGE-QUOTA = <integer 0..99>
New percentage of main memory which is to be used for big pages.
REDUCE-BIG-PAGES = *UNCHANGED / *NO / list-poss(2): *ON-QUOTA-EXCESS / *ON-CORE-SATURATION
Specifies whether and in which situation big pages may be reduced and become available as normal main memory.
The default is *UNCHANGED, i.e. the setting is not modified.
REDUCE-BIG-PAGES = *NO
Big pages are never reduced.
REDUCE-BIG-PAGES = *ON-QUOTA-EXCESS
Big pages are to be reduced if the existing size of the big page memory exceeds the percentage assigned (see BIG-PAGE-QUOTA).
REDUCE-BIG-PAGES = *ON-CORE-SATURATION
Big pages are to be reduced only if there is a threat of CORE saturation but this can be prevented by canceling a big page in the normal main memory. This value is also set at system startup.
The two reduction situations *ON-QUOTA-EXCESS and *ON-CORE-SATURATION can be combined by being specified in a list.
EXTEND-BIG-PAGES = *UNCHANGED / *NO / list-poss(2): *ON-QUOTA-DEFICIENCY /
*ON-BIG-PAGE-SATURATION
Specifies if and in which situation big pages are expanded. Additional big pages reduce the available normal main memory accordingly.
The default is *UNCHANGED, i.e. the setting is not modified.
EXTEND-BIG-PAGES = *NO
Big pages should never be extended; that is, neither when below the BIG-PAGE-QUOTA nor in case of memory saturation of the big page memory.
EXTEND-BIG-PAGES = *ON-QUOTA-DEFICIENCY
Big pages are only to be extended if the existing size of the big page memory exceeds the percentage assigned (see BIG-PAGE-QUOTA).
EXTEND-BIG-PAGES = *ON-BIG-PAGE-SATURATION
Big pages are only to be extended if there is an insufficient number of free big pages. By this, however, the should-be value for big pages defined by the big page quota will not be exceeded, meaning the actual value is smaller than the should-be value because previously big pages were broken up due to a memory saturation or because the actual value has so far not reached the should-be value. The latter is dependent on the memory sizes under and over the memory minimum and/or the number of logical machines (CPU). This is also the value set at system startup.
The two reduction situations *ON-QUOTA-DEFICIENCY and *ON-BIG-PAGE-SATURATION can be combined by being specified in a list.
Return codes
(SC2) | SC1 | Maincode | Meaning/Guaranteed messages |
|---|---|---|---|
0 | CMD0001 | Command executed | |
1 | 0 | CMD0001 | Warning: Operation has already taken place for object or no action was required |
2 | 0 | CMD0001 | Warning: Operation has already taken place for object but could have negative consequences |
1 | CMD2201 | Interface error between SDF and command server | |
3 | CMD2203 | SDF version not supported | |
32 | EMM2800 | Internal error | |
64 | CMD0216 | Privilege error | |
130 | EMM2807 | Operation cannot be executed due to lack of resources |