HP-UX Reference (11i v1 05/09) - 5 Miscellaneous Topics (vol 9)

m
max_mem_window(5) max_mem_window(5)
(Tunable Kernel Parameters)
NAME
max_mem_window - maximum number of group-private 32-bit shared memory configurable by users
VALUES
Default
0
Allowed values
Minimum: 0 shared memory windows
Maximum: 8192 shared memory windows
DESCRIPTION
Processes in a PA-RISC 32-bit architecture usually share the global quadrants 3 and 4 for such things as
I/O mappings, shared libraries, shared mapped files, etc. However, you may wish to use quadrant 3 in a
more limited sharing fashion with only a select group of processes. Memory windows allow this functional-
ity.
If this tunable is set to 0, 32-bit programs always use the global Q3 and Q4 for shared memory. If this tun-
able is greater than 0 processes in defined groups use a Q3 private to that group, and then the globally
shared Q4 if Q3 is full.
Who is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
When Should the Value of This Tunable Be Raised?
This tunable should only be raised if more group-private Q3 areas are needed by the system users. If more
areas are not needed, there is literally no point to raising this value.
What Are the Side Effects of Raising the Value?
The kernel will require additional memory to support the additional memory windows. Depending on the
value of shmmni or (if ShmemExtensions is installed on the system)
shmmni_extended, this amount of
memory may be non-trivial. Strong caution is urged before arbitrary raising of this tunable as a result. If
the number of identifiers is set to 8,192 each memory window added to the system requires an additional
.25 Mb of memory. If the number of identifiers is set to 32,768 this increases to 1 Mb per memory window.
Memory pressure caused by setting these tunables too high for the available memory on the system may
cause inordinate paging, performance degradation or failure to boot the system entirely due to insufficient
free memory.
When Should the Value of This Tunable Be Lowered?
If process groups are not being used, or not being used in the quantity set by the tunable, there is really no
point to having this value higher than what is actually needed.
What Are the Side Effects of Lowering the Value?
The kernel uses less memory. If the value is set to
0, no group-private Q3’s are allowed.
What Other Tunable Values Should Be Changed at the Same Time?
None.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its
meaning changed in future releases of HP-UX.
AUTHOR
max_mem_window was developed by HP.
SEE ALSO
shmmni(5).
Section 5−−96 Hewlett-Packard Company − 1 − HP-UX 11i Version 1: September 2005