allocate_fs_swapmap(5)                               allocate_fs_swapmap(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      allocate_fs_swapmap - determines when swapmap structures are allocated
      for filesystem swap

 VALUES    [Toc]    [Back]
    Failsafe
      0 (off)

    Default    [Toc]    [Back]
      0 (off)

    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
      contention.

      Dynamic allocation decreases the memory footprint of the filesystem
      swap system.

    Who is Expected to Change This Tunable?
      Anyone.

    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
      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.




 Hewlett-Packard Company            - 1 -      HP-UX 11i Version 2: Sep 2004






 allocate_fs_swapmap(5)                               allocate_fs_swapmap(5)
                          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?
      None.

 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
      http://docs.hp.com.

 AUTHOR    [Toc]    [Back]
      allocate_fs_swapmap was developed by HP.


 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004