Extra swapping when using gfortran 4.3-20061224 vs gfortran 4.2-20061211

[Toon Moene <toon at moene dot indiv dot nluug dot nl>]

A run of HIRLAM for which the grid was carefully tuned (half a year ago) 
to the RAM size of my laptop suddenly started to swap two weeks ago when 
using gfortran 4.3 as the compiler.

However, as the HIRLAM suite I'm testing with also constantly changes, I 
first suspected our own source code.  Today I finished the back-to-back 
comparison of gfortran 4.3-20061224 vs. gfortran 4.2-20061211. 
Compiling all the source with the first (experimental) compiler makes 
HIRLAM swap during execution, whereas with the second (prerelease) 
compiler, it doesn't.

The code basically processes all of about 450 Mbyte of arrays every 16.5 
seconds (the time step).  Every 12 time steps it performs output worth 
1/2 to 13 Mbyte of Fortran unformatted direct access files.  There is 
also a small amount of formatted sequential output to be able to monitor 
the progress of the model integration.

Is something changed in the buffering of output, or is there another 
change in handling of temporary arrays that could explain this phenomenon ?

Thanks in advance for any insight.

--
Toon Moene - e-mail: toon@moene.indiv.nluug.nl - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
A maintainer of GNU Fortran: http://gcc.gnu.org/fortran/
Who's working on GNU Fortran: 
http://gcc.gnu.org/ml/gcc/2006-01/msg00000.html