maxdsiz(5)                                                       maxdsiz(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      maxdsiz, maxdsiz_64bit - maximum size (in bytes) of the data segment
      for any user process

 VALUES    [Toc]    [Back]
    Default
      32bit: 1 GB

      64bit: 4 GB

    Allowed values    [Toc]    [Back]
      32 bit minimum: 0x40000

      32 bit maximum: 0xfffff000

      64 bit minimum: 0x40000

      64 bit maximum: 0x3ffbffff000

 DESCRIPTION    [Toc]    [Back]
      User programs on HP-UX systems are composed of five discrete segments
      of virtual memory: text (or code), data, stack, shared, and I/O.  Each
      segment occupies an architecturally defined range of the virtual
      address space that sets the upper limit to their size, but text, data
      and stack segments may have smaller maxima enforced by the maxtsiz,
      maxdsiz, and maxssiz tunables.

      This tunable defines the maximum size of the static data storage
      segment for 32-bit and 64-bit processes.  The data storage segment
      contains fixed data storage such as globals, arrays, static variables,
      local variables in main(), strings, and space allocated using sbrk()
      and malloc().  In addition, any files memory mapped as private and
      shared library per-invocation data also resides in the data segment.

    Who is Expected to Change This Tunable?
      Anyone.

    Restrictions on Changing    [Toc]    [Back]
      Changes to this tunable take effect only for processes started after
      the modification. In addition, a process which modifies it's rlimit
      for the data segment propagates the modified limit to all child
      processes, thereby exempting them from any future modification of
      maxdsiz.

    When Should the Value of This Tunable Be Raised?
      This tunable should be raised if user processes are receiving the
      [ENOMEM] error message:

           exec(2): data exceeds maxdsiz





 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003






 maxdsiz(5)                                                       maxdsiz(5)
                          Tunable Kernel Parameters



      or

           exec(2): data exceeds maxdsiz_64bit.

      This may or may not cause a process failure depending on the program
      code.

    What Are the Side Effects of Raising the Value?
      Raising this tunable by definition allows larger data segments for
      every process.  The maxdsiz and maxssiz tunables limit the amount of
      swap space that can be reserved or used by each process, but using
      more virtual address space does not translate directly into using more
      physical address space because virtual pages can be swapped out.

      Note that if swap space on the machine is near capacity, raising this
      tunable increases the amount of reservable swap per process.  This
      could exhaust the swap space on the system by allowing a process with
      a memory leak or a malicious program that uses huge amounts of memory
      to reserve too much swap space.

    When Should the Value of This Tunable Be Lowered?
      This tunable should be lowered if swap space is at a premium on the
      machine and programs that are using too much swap space are affecting
      the execution of other critical user processes.

    What Are the Side Effects of Lowering the Value?
      If swap space on the machine is near capacity, lowering this tunable
      will limit the amount of swap reserved for each process and will cause
      the processes that consume large amounts of swap space to receive the
      [ENOMEM] error.

    What Other Tunable Values Should Be Changed at the Same Time?
      The maxssiz tunable should be considered because it too limits swap
      usage by process stack segment.

 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.

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

 SEE ALSO    [Toc]    [Back]
      getrlimit(2), setrlimit(2), maxtsiz(5), maxssiz(5).


 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003