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Subject: Re: [OMPI devel] Possible memory leak
From: Sylvain Jeaugey (sylvain.jeaugey_at_[hidden])
Date: 2010-09-01 04:07:36

Hi ananda,

I didn't try to run your program, but this seems logical to me.

The problem with calling MPI_Bcast repeatedly is that you may have an
infinite desynchronization between the sender and the receiver(s).
MPI_Bcast is an unidirectional operation. It does not necessary block
until the receiver(s) gets the message, hence causing a huge number of
messages to be buffered (and in the case of ft-enable-cr, I guess
everything is saved until an operation going the other way is done).

To "solve" this issue, the sync collective component has been created to
perform a barrier every N operations. So, running with -mca coll
basic,sync should make the problem disappear. I don't think it is really a
memory leak, the memory used is needed (in case of fault) and should be
freed at the next operation going the other way (reduce, barrier,

This seems to be the classical problem of MPI_Bcast benchmarks. Real
applications usually don't suffer this kind of problems.


On Tue, 31 Aug 2010, ananda.mudar_at_[hidden] wrote:

> Hi
> When I run the attached program with the following arguments, the size of MPI processes keep increasing alarmingly (I saw that the size grew from 18M to 12G in under 10 minutes) making me suspect that there is a major memory leak:
> mpirun -am ft-enable-cr --mca coll basic -np 2 <name of the executable>
> If I run this program without checkpoint control ie; remove "-am ft-enable-cr", the size of MPI processes stays constant.
> Also if I run this program without setting "--mca coll basic", the size of the MPI processes stays constant.
> I set the mca parameter to "--mca coll basic" during my debugging attempts of the problem related to checkpointing the program that has repetitive MPI_Bcast() calls.
> FYI, I am using OpenMPI v1.4.2 with BLCR 0.8.2
> Thanks
> Ananda
> Ananda B Mudar, PMP
> Senior Technical Architect
> Wipro Technologies
> Ph: 972 765 8093
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