IRIS Performer requires shared memory and uses a memory-mapped
  file, the location of which depends on the value of the PFTMPDIR
  environment variable:

  If PFTMPDIR is not set, Performer uses /dev/zero as the default.
  Running an application in this configuration:

    - Uses swap space 
    - Does not require disk space until main memory is exhausted 
    - Is faster than using a regular memory mapped file via PFTMPDIR 
    - Causes IRIX to kill the process(es) and log an error to the
      console if the application runs out of space for shared memory in
      the swap partition.

  If PFTMPDIR is set, Performer creates files in the specified
  directory. Running an application in this configuration:

    - Requires disk space even before main memory is exhausted 
    - Is slower than /dev/zero because it touches the disk 
    - Produces appropriately sized core dump files with no limit set by
      IRIS Performer
    - Might cause a core dump from a segmentation violation inside
      pfMalloc if the application runs out of space for shared memory
      in the file system containing PFTMPDIR
    - PFTMPDIR should be set only to a directory on a local file system.