03-19-2012
All memory is backed by swap whether it's needed right this moment or not. So the swap space isn't actually being used at present -- but if memory became short, everything already has preallocated locations in swap to get dumped into.
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LEARN ABOUT HPUX
allocate_fs_swapmap
allocate_fs_swapmap(5) File Formats Manual allocate_fs_swapmap(5)
NAME
allocate_fs_swapmap - determines when swapmap structures are allocated for filesystem swap
VALUES
Failsafe
Default
Allowed values
or
DESCRIPTION
The tunable is used to determine whether to allocate all needed filesystem swap structures during the initialization of the filesystem swap
device or wait until they are needed. Pre-allocation of all filesystem swap structures upon initialization saves time during later usage
of the filesystem swap, and prevents later allocation failure due to physical memory contention.
Dynamic allocation decreases the memory footprint of the filesystem swap system.
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?
Systems under heavy memory load may not be able to acquire enough memory to hold the swap mapping structures for an addition of file system
swap. These calls to add swap would fail with the error though presumably they would be retried. Frequent failure on file system swap
addition with would merit enabling this tunable.
What Are the Side Effects of Raising the Value?
All the swap map structures for each file system swap device would be preallocated during swap initialization at kernel boot, increasing
the memory footprint of the kernel. The amount of increase depends on the number and size of file system swap devices.
When Should the Value of This Tunable Be Lowered?
Systems with limited memory available to the kernel that also have limited use of file system swap devices should disable this tunable to
decrease kernel memory usage.
What Are the Side Effects of Lowering the Value?
File system swap additions may fail with when memory contention is high.
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 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 tun-
able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was
factory installed on your system, see at
AUTHOR
was developed by HP.
Tunable Kernel Parameters allocate_fs_swapmap(5)