allocate_fs_swapmap(5)allocate_fs_swapmap(5)NAMEallocate_fs_swapmap - determines when swapmap structures are allocated
for filesystem swap
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
Who is Expected to Change This Tunable?
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 mem‐
ory to hold the swap mapping structures for an addition of file system
swap. These calls to add swap would fail with the error though presum‐
ably they would be retried. Frequent failure on file system swap addi‐
tion 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 lim‐
ited 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
What Other Tunable Values Should Be Changed at the Same Time?
All HP-UX kernel tunable parameters are release specific. This parame‐
ter may be removed or have its meaning changed in future releases of
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 val‐
ues. For information about the effects of installation on tunable val‐
ues, consult the documentation for the kernel software being installed.
For information about optional kernel software that was factory
installed on your system, see at
was developed by HP.
Tunable Kernel Parameters allocate_fs_swapmap(5)