If you need to support more attachments you can set the value of that variable 
either by setting:



mpirun command line:

—mca osc_rdma_max_attach

Keep in mind that each attachment may use an underlying hardware resource that 
may be easy to exhaust (hence the low default limit). It is recommended to keep 
the total number as small as possible.


> On Jan 8, 2019, at 9:36 PM, Udayanga Wickramasinghe <uswic...@iu.edu> wrote:
> Hi,
> I am running into an issue in open-mpi where it crashes abruptly during 
> [nid00307:25463] *** An error occurred in MPI_Win_attach
> [nid00307:25463] *** reported by process [140736284524545,140728898420736]
> [nid00307:25463] *** on win rdma window 3
> [nid00307:25463] *** MPI_ERR_RMA_ATTACH: Could not attach RMA segment
> [nid00307:25463] *** MPI_ERRORS_ARE_FATAL (processes in this win will now 
> abort,
> [nid00307:25463] ***    and potentially your MPI job)
> Looking more into this issue, it seems like open-mpi has a restriction on the 
> maximum number of segments attached to 32. (OpenMpi3.0 spec doesn't spec 
> doesn't say a lot about this scenario --"The argument win must be a window 
> that was created with MPI_WIN_CREATE_DYNAMIC. Multiple (but nonoverlapping) 
> memory regions may be attached to the same window")
> To workaround this, I have temporarily modified the variable 
> mca_osc_rdma_component.max_attach. Is there any way to configure this in 
> open-mpi?
> Thanks
> Udayanga
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