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<p><font size="4">Can somebody help me understand this "smaller memory footprint" issue that is part f the subsetting goal better. What systems does it affect? What does "memory footprint" really mean? In the 64 bit address space, virtual address range is not a problem.<br>
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On systems I am most familiar with (AIX and I have been told Linux too), if you have a library that contains 1000 subroutines and you run a program than only calls 6 then only the pages that are touched by code for those 6 functions must get placed in real memory. The rest of the object code stays on disk. Program and library text is demand paged. The loading is on page boundries, not subroutine boundries. </font><br>
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With a shared library, if I run a program on a node and touch 6 subroutines and you run a different program that touches those 6 and 10 more then code for all 16 subroutines may be kept in memory but the rest of the library will stay on disk. You and I will share the object code for the 6 subroutines we are both calling.<br>
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<font size="4">Someone who wanted to make a libmpi that has MPI-1sided or MPI-IO well isolated in the library structure so simple MPI jobs would not force this extra code into memory could do that today. The user does not need to promise not to call MPI-IO subroutines for them not to to take real memory. The "subsets" would need to be devised by the MPI implementor but would be transparent to the MPI user and not dictated by the standard. The "subsets" the user did not call would remain paged out.</font><br>
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Perhaps all static data defined by the library will come into real memory for each process but is there much reduction from being able to somehow not bring in the static data MPI-IO would require because somebody had promised not to use it?<br>
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Dick </font><br>
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Dick Treumann - MPI Team/TCEM <br>
IBM Systems & Technology Group<br>
Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601<br>
Tele (845) 433-7846 Fax (845) 433-8363<br>
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