NAME
allocate_fs_swapmap — determines when swapmap structures are allocated for filesystem swap
VALUES
Allowed values
1 (on)
or
0 (off)
DESCRIPTION
The
allocate_fs_swapmap
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
ENOMEM,
though presumably they would be retried.
Frequent failure on file system swap addition with
ENOMEM
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
ENOMEM
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 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://docs.hp.com.
AUTHOR
allocate_fs_swapmap
was developed by HP.
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