Tunable Kernel Parameters
NAME [Toc] [Back]
allocate_fs_swapmap - determines when swapmap structures are allocated
for filesystem swap
VALUES [Toc] [Back]
Default [Toc] [Back]
Allowed values [Toc] [Back]
1 (on) or 0 (off)
DESCRIPTION [Toc] [Back]
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
Dynamic allocation decreases the memory footprint of the filesystem
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?
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
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.
Hewlett-Packard Company - 1 - HP-UX 11i Version 2: Sep 2004
Tunable Kernel Parameters
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?
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]
allocate_fs_swapmap was developed by HP.
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: Sep 2004 [ Back ]