[mpich-discuss] MPI memory allocation.

Rajeev Thakur thakur at mcs.anl.gov
Thu Dec 5 15:01:39 CST 2013

The master is receiving too many incoming messages than it can match quickly enough with Irecvs. Try using MPI_Issend instead of MPI_Isend.


On Dec 5, 2013, at 2:58 AM, Anatoly G <anatolyrishon at gmail.com> wrote:

> Hello.
> I"m using MPICH2 1.5.
> My system contains master and 16 slaves. 
> System uses number of communicators.
> The single communicator used for below scenario:
> Each slave sends non-stop 2Kbyte data buffer using MPI_Isend and waits using MPI_Wait.
> Master starts with MPI_Irecv to each slave
> Then in endless loop:
> MPI_Waitany and MPI_Irecv on rank returned by MPI_Waitany.
> Another communicator used for broadcast communication (commands between master + slaves), 
> but it's not used in parallel with previous communicator, 
> only before or after data transfer.
> The system executed on two computers linked by 1Gbit/s Ethernet.
> Master executed on first computer, all slaves on other one.
> Network traffic is ~800Mbit/s.
> After 1-2 minutes of execution, master process starts to increase it's memory allocation and network traffic becomes low.
> This memory allocation & network traffic slow down continues until fail of MPI, 
> without core file save.
> My program doesn't allocate memory. Can you please explain this behaviour.
> How can I cause MPI to stop sending slaves if Master can't serve such traffic, instead of memory allocation and fail?
> Thank you,
> Anatoly.
> P.S.
> On my stand alone test, I simulate similar behaviour, but with single thread on each process (master & hosts).
> When I start stand alone test, master stops slaves until it completes accumulated data processing and MPI doesn't increase memory allocation.
> When Master is free slaves continue to send data.
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