[Pw_forum] Off-topic: memory usage issues

[Marcos Verissimo Alves]

Hi all,

This is not a question specifically aimed at espresso issues, but since we
have quite a few knowledgeable people in the list, I'm posting it.

I have compiled pw.x in a dual-core Turion with 2GB RAM under linux
(OpenSuse 10.2), installed and compiled mpich 2-1.0.5 with ifort 9.1.041,
and then compiled pw.x (from Espresso 3.0) with mpich, mkl 8.0 and fftw,
and I have been running it successfully since then in parallel. However,
looking at the memory usage using top, when running pw.x, I see that,
although the memory from top is at most 250 MB per processor (from the
part where the individual processes' cpu and memory usage is displayed),
almost the whole of physical memory is taken (from the "Mem: total, used,
free, buffers" line).

Right after the booting of the machine, the total memory taken by the
system processes is 230 MB (I'm running it without the X-windows system to
make the most possible memory available to the calculations). When I run
pw.x in the two processors, each process takes 298 MB of virtual memory,
according to top. Thus, there should be only around 830 MB (596 + 230 MB)
used, but about 1650 MB are taken. Running pw.x in serial mode (that is,
the same compilation, but without invoking mpirun or mpiexec) has the same
effect: the total virtual memory is 532 MB, but 367 MB.

The same kind of thing happens when I run another DFT code (siesta), so I
would guess this could be an MPICH-related issue or, worse, a kernel- or
compiler-related issue. Does anyone know if there are any memory-usage
issues for MPICH, for the newer versions of the linux kernel or for the
ifort 9.1.041/mkl 8.0? Has anybody seen something similar when running
pw.x on dual-processor machines?

Thanks,

Marcos

-- 
Dr. Marcos Verissimo Alves
Post-Doctoral Fellow
Condensed Matter and Statistical Physics Sector
International Centre for Theoretical Physics
Trieste, Italy

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