[Pw_forum] ifc/linux allocation of more than 2 GB dynamical memory

[Nicola Marzari]

Dear All,

we have recently realized that there is an issue running large jobs
on Linux machines, and I was wondering if anyone had some suggestions.

This is the problem: if a fortran code running under Linux
(Red Hat 9) and using ifc (7.1) and mkl (6.0) tries to allocate
a number of arrays that total over 2 GB, it ends with a runtime error.

This happens no matter the amount of dynamical memory physically
available (we tested this on a machine having ~4GB RAM), and happens
exactly at the point in which the array that is being allocated
overshoots 2GB .

The Intel webpage has a comment somewhere mentioning this limitation,
suggesting it is related to where the kernel allocates space for the
linked libraries, but we have had no success trying their suggestions
(e.g. compiling -static).

In practice, this limitation is even more serious, since a running
code (e.g. CP) that allocates ~< 2GB will only use, in runtime, an
average value that is smaller (~1.25GB).

Any helpful suggestions would be very welcome,


			nicola

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Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758  fax 617.2586534  marzari at mit.edu  http://nnn.mit.edu