Tunable Kernel Parameters
NAME [Toc] [Back]
unlockable_mem - amount of physical memory that may not be locked by
VALUES [Toc] [Back]
Allowed values [Toc] [Back]
Minimum: 0 pages
Maximum: Any value less than the available physical memory.
If unlockable_mem is set less than or equal to 0 (such as the default
value), the kernel uses the value of:
(200 + UPAGES / 2) * (number-of-enabled-processors)
where UPAGES is the minimum amount of pages for thread user areas, and
is set to 4 on 32-bit PA-RISC architectures, and 8 on 64-bit PA-RISC.
On the Itanium(R)-based architecture, UPAGES is the sum of the pages
needed for the RSE stack, the traditional stack, the stack red zone
(between the traditional and RSE stacks) and the size of the usual
DESCRIPTION [Toc] [Back]
Memory locking allows the privileged user to specify which pages need
to remain in memory, and unaffected by the swap process. This feature
allows you to ensure that memory access times are unaffected by delays
introduced by memory paging and swapping. For example, locking is a
tool provided to privileged users on a system that is short on
physical memory. Instead of having these privileged processes swap
like the rest of the processes, they can lock portions of their
address space. Once the pages are locked in for the privileged
processes, they will no longer have to worry about memory contention.
The unprivileged processes however, will have to compete for memory.
unlockable_mem provides you with a limiting factor on this privileged
behavior, by setting the amount of memory which cannot be locked by
Who is Expected to Change This Tunable?
Restrictions on Changing [Toc] [Back]
Changes to this tunable take effect at the next reboot.
When Should the Value of This Tunable Be Raised?
This tunable should be raised on systems operating with low available
physical memory where privileged processes are using memory which
would be better used by processes which are considered more important,
Hewlett-Packard Company - 1 - HP-UX 11i Version 2: Sep 2004
Tunable Kernel Parameters
but which do not lock memory. Raising the tunable would force less
pages locked and therefore usable by all processes.
Notice that none of this makes any difference to the kernel itself as
it can steal pages from the locked pool when it needs to.
What Are the Side Effects of Raising the Value?
Processes which seek to lock their memory have a smaller pool to work
in, and if large amounts of locked memory are requested and the pages
are simply in use, lock operations will fail. How the process handles
the failure will vary by implementation.
When Should the Value of This Tunable Be Lowered?
If the lockable memory pool is smaller than the demand, processes
requesting locked memory will fail. Lowering unlockable_mem will
provide more lockable memory.
What Are the Side Effects of Lowering the Value?
Processes which do not use locked memory will be more likely to swap
since less memory is available to the system for general usage, if
privileged processes have locked the increased space in their pool.
What Other Tunable Values Should Be Changed at the Same Time?
WARNINGS [Toc] [Back]
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 parameter 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
AUTHOR [Toc] [Back]
unlockable_mem was developed by HP.
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: Sep 2004 [ Back ]