nsysmap(5)                                                       nsysmap(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      nsysmap, nsysmap64 - number of entries in a kernel dynamic memory
      allocation map

 VALUES    [Toc]    [Back]
    Default
      8400

    Allowed Values    [Toc]    [Back]
      Any positive value.

      In practice, very small values will likely cause a panic during boot
      (or soon after) and very large values are probably unnecessary.
      Changing the tunable from the default is only necessary under certain
      conditions.

 DESCRIPTION    [Toc]    [Back]
      This value sizes the kernel dynamic memory resource map, an array of
      address/length pairs that describe the free virtual space in the
      kernel's dynamic address space.

      This array has historically been statically-sized.  That means certain
      pathological workloads that fragment the kernel address space will
      result in too many entries for the array.  Rather than panicking when
      this condition occurs, the system throws away the last entry, which
      results in "leaked" kernel virtual address space.  If this overflow
      happens often enough, the system eventually runs out of virtual space
      and will panic with the following message:

           kalloc: out of virtual space.

      By making the map size tunable, the system can automatically scale the
      map size according to the system workload size and avoid this problem.
      If the automatic scaling does not work, you can hand-tune to fit a
      particular workload.  When the default value is overridden, the kernel
      may increase the value beyond the your specification depending on the
      system size.

      There are different tunables for 32- and 64-bit kernel because the
      64-bit kernel has more virtual address space.  The nsysmap tunable
      controls 32-bit kernels and the nsysmap64 tunable controls 64-bit
      kernels.

    Who Is Expected to Change This Tunable?
      Only those experiencing the resource map overflow will need to modify
      this tunable.

    Restrictions on Changing    [Toc]    [Back]
      Changes to this tunable take effect at the next reboot.





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






 nsysmap(5)                                                       nsysmap(5)
                          Tunable Kernel Parameters



    When Should the Value of This Tunable Be Raised?
      The following message will appear on the console when the resource map
      overflow occurs: sysmap{32|64}: rmap ovflo, lost [X,Y).

      If this happens only occasionally, no action is necessary.  If this
      happens with any sort of frequency, the tunable should be increased,
      or the following panic message may occur:

           kalloc: out of kernel virtual space.

      When increasing nsysmap{32|64}, doubling the tunable value is a
      reasonable rule of thumb.  If the problem persists after doubling the
      tunable several times from the default, there is likely to be a more
      serious kernel problem, and you should contact HP support to
      investigate.

    What Are the Side Effects of Raising the Value of This Tunable?
      Kernel memory use increases very slightly.  Depending on the workload,
      if the tunable is quite large, the performance of kernel memory
      allocation may be affected.

    When Should the Value of This Tunable Be Lowered?
      Lowering this tunable from the default is risky, in all probability
      unnecessary, and should only be done after first consulting HP
      support.

    What Are the Side Effects of Lowering the Value of This Tunable?
      A much higher probability of resource map overflows eventually leading
      to a kernel panic.

    What Other Tunables 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]
      nsysmap and nsysmap64 were developed by HP.


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