
    Driver Program for IBM's xl-Compiler series
    ===========================================

    This programm is used to call compilers on RS/6000 under AIX.

    It changes the data segment size limit to "unlimited" before
    starting the original compiler driver program.

    The reason for this arises mainly when the RS/6000 are used in
    batch mode.
    Since it is of high interest not to overload the machines real
    memory, a batch system should - well our's does - take into
    account the memory claimed by all jobs currently under execution.
    In almost every case the code size is neglectible compared to
    the amount of data, so the data segment size has been well
    established for batch planning purposes.

    On the other hand, when one dares to have a look at (e.g.)
    /usr/lpp/xlf/bin/xlfentry which is the "real" compiler (xlf is only
    the driver front end), the "size" command tells that a "bss"
    (i.e. "uninitialized data segment") of approx. 160 MB is defined
    for xl-Fortran Version 2 Release 3 and approx. 500 MB for xl-Fortran
    Version 3 Release 1 (We've never seen a compiler run exceeding a few MB).
    
    No doubt, the data segment size limit must be at least these
    500 MB to run the compiler - and exactly that makes planning of
    batch jobs impossible since it's impossible for the batch scheduler 
    to know whether a job has claimed 500mb just to compile a "hello world",
    or whether this amount of data will be really used for a computation.

    Due to the fact that it cannot be avoided to compile during
    the progress of computations (as required by many software
    application products) one cannot circumvent the limit by compiling
    interactively and just submitting the executable.

    Therefore without this program you can decide whether you prefer not to
    compile within batch jobs or not to restrict memory consumption
    and thus rely on the "good behaviour" of Your users, with the
    risc in mind that the machine's memory will get highly overloaded.

    NOTE (special hint to IBM programmers)
    This is a WORKARROUND, NOT the solution of the problem.


    Thomas Eifert, ReZe, RWTH Aachen, Germany
		eifert@rz.RWTH-Aachen.DE
    Ingo Schneider, ReZe, RWTH Aachen, Germany    
		schneider@rz.RWTH-Aachen.DE



