mprotect_reduce_protid_on.5 (2011 03)

m
mprotect_reduce_protid_on(5) mprotect_reduce_protid_on(5)
(Tunable Kernel Parameters)
NAME
mprotect_reduce_protid_on - reduces protection IDs/keys usage for shared memory segments
VALUES
Failsafe
0 (off)
Default
0 (off)
Allowed values
0 (off) or 1 (on).
DESCRIPTION
The
mprotect_reduce_protid_on
tunable is provided to reduce user application’s protection
IDs/keys usage for shared memory segments.
When an application uses mprotect (2) extensively on a shared memory (shmget(2)), this may lead to a
huge number of protection IDs/keys being assigned to the application and may also increase the size of
the data structure where this information is maintained. This may result in application performance
degradation.
When the
mprotect_reduce_protid_on
tunable is turned on, it tries to reduce the number of pro-
tection IDs/keys being allocated to user applications. This tunable also attempts to optimize the way the
information on protection IDs/key is maintained. Overall, using this tunable can typically help in
improving user application’s performance.
However, when the tunable is turned on, there are situations when it may not improve or may actually
degrade the application’s performance. This may happen due to the overhead involved in reducing the
number of protection IDs/keys.
The overall performance depends on the nature of the application. This tunable may work with some
applications and may not work with others. Although it attempts to improve the performance of the appli-
cation, it may result in application performance degradation or no improvement at all.
Who Is Expected to Change This Tunable?
Anyone with super-user privileges.
Restrictions on Changing
Changes to this tunable take effect immediately.
When Should the Value of This Tunable Be Raised?
When you observe that the application’s performance is getting degraded due to extensive usage of mpro-
tect (2) on shared memory segments.
What are the Side Effects of Raising the Value?
When turned on, it may sometime reduce overall system performance.
When Should the Value of This Tunable Be Lowered?
When you observe degradation when the tunable is turned on.
What are the Side Effects of Lowering the Value?
The original behavior is retained.
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.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-
ter values. After installation, some tunable parameters may no longer be at the default or recommended
values. For information about the effects of installation on tunable values, consult the documentation for
the kernel software being installed. For information about optional kernel software that was factory
installed on your system, see HP-UX Release Notes at
http://www.hp.com/go/hpux-core-docs.
HP-UX 11i Version 3: March 2011 − 1 − Hewlett-Packard Company 1