eqmemsize(5)                                                   eqmemsize(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      eqmemsize - determines the minimum size (in pages) of the equivalently
      mapped reserve pool

 VALUES    [Toc]    [Back]
    Default
      15 pages

    Allowed values    [Toc]    [Back]
      0 or any positive integer.

      However, because this represents physical pages no longer available
      for general system use, caution is urged before using large values.

 DESCRIPTION    [Toc]    [Back]
      Equivalently mapped memory is a page which has the same physical and
      virtual address.  This is useful for some applications, and for I/O.
      Since most memory is to be used in the traditional swapper/virtual
      address model, it is useful for the system to reserve some pages for
      this type of access at boot while the most physical memory is
      available.

      eqmemsize provides the bottom value for the size of this reserved
      pool.  The actual pool size is the sum of eqmemsize and a value
      determined dynamically at boot using the available size of physical
      memory, to account for large memory systems automatically.  The scaled
      value increases the pool size by 1 page per 256 MB.

    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?
      This tunable should raised if the customer sees the error message:

          Equivalently mapped reserve pool exhausted;

          Overall application performance may be improved by    [Toc]    [Back]

          increasing the "eqmemsize" tunable parameter

          (currently set to "{X}").

    What Are the Side Effects of Raising the Value?
      Physical memory is reserved for this use and unavailable for the rest
      of the system.  Increasing this tunable by a substantial amount would
      be roughly equivalent to removing the same amount of physical memory.
      The amount of memory represented by the increase in the tunable is not
      likely to be used for equivalent memory, and no one else can get to



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






 eqmemsize(5)                                                   eqmemsize(5)
                          Tunable Kernel Parameters



      this memory either.

    When Should the Value of This Tunable Be Lowered?
      In general, if the tunable is set to more than 10 pages over
      15+(physical_memory/256 MB), it's probably too high.  Specifically, if
      the system swaps heavily, and the above is true, the value should be
      lowered to free the physical memory back to the system.

    What Are the Side Effects of Lowering the Value?
      Requests for equivalent memory may be denied.  This is not a fatal
      error, but it should be avoided.

    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]
      eqmemsize was developed by HP.


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