I'm using openmpi-1.1 on a linux-amd64 machine and also a linux-32bit x86
chroot environment on that same machine.
(distro is gentoo, compilers: gcc-4.1.1 and gcc-3.4.6)
In both cases openmpi-1.1 shows a +/-400MB overhead in virtual memory usage
(virtual address space usage) for each MPI process.
In my case this is quite troublesome because my application in 32bit mode is
counting on using the whole 4GB address space for the problem set size and
This means that I have a reduction in the size of the problems which it can
(my aplication isn't 64bit safe yet, so I need to run in 32bit mode, and use
effectively the 4GB address space)
Is there a way to tweak this overhead, by configuring openmpi to use smaller
buffers, or anything else ?
I do not see this with mpich2.
Miguel Sousa Filipe