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<DIV dir=ltr align=left><SPAN class=308412821-08052008></SPAN><FONT
face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=308412821-08052008>Dear
Dick,</SPAN></FONT></FONT></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=308412821-08052008></SPAN></FONT></FONT></FONT> </DIV>
<DIV dir=ltr align=left><FONT><FONT><FONT face=Arial><FONT color=#0000ff><FONT
size=2>By the looks of it, MPI-3 is going to be big.<SPAN
class=308412821-08052008> </SPAN>P<SPAN class=308412821-08052008>etascale
machines may not have OS we're accustomed to, dynamic libraries, and some other
things. Smaller system libraries - and smaller MPI - may be needed there. Some
of the envisioned MPI-3 features will be needed for some applications, some
won't. Same with MPI-2 and MPI-1. Defining subsets may help to open a way to
custom cut MPI libraries suitable for particular application classes. How
subsets will be implemented is a different
matter.</SPAN></FONT></FONT></FONT></FONT></FONT></DIV>
<DIV dir=ltr align=left><FONT><FONT><FONT face=Arial><FONT color=#0000ff><FONT
size=2><SPAN
class=308412821-08052008></SPAN></FONT></FONT></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=308412821-08052008>Best regards.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=308412821-08052008></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=308412821-08052008>Alexander</SPAN></FONT></FONT></FONT></DIV>
<DIV dir=ltr align=left><BR></DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> mpi-22-bounces@lists.mpi-forum.org
[mailto:mpi-22-bounces@lists.mpi-forum.org] <B>On Behalf Of </B>Richard
Treumann<BR><B>Sent:</B> Thursday, May 08, 2008 11:23 PM<BR><B>To:</B> MPI
2.2<BR><B>Subject:</B> [Mpi-22] Memory footprint concern<BR></FONT><BR></DIV>
<DIV></DIV>
<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><BR>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><FONT
size=4><BR>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></FONT><BR><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><FONT size=4><BR>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><BR>Dick </FONT><BR><BR>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></P><pre>---------------------------------------------------------------------
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