Jeff, At first glance, a comment in the code suggests the rationale is to minimize the number of allocations and hence the time spent registering the memory.
Cheers, Gilles Jeff Hammond <jeff.scie...@gmail.com> wrote: >Why is this allocated statically? I dont understand the difficulty of a >dynamically allocates and thus unrestricted implementation. Is there some >performance advantage to a bounded static allocation? Or is it that you use >O(n) lookups and need to keep n small to avoid exposing that to users? > > >I have usage models with thousands of attached segments, hence need to >understand how bad this will be with Open-MPI (yes I can amortize overhead but >it’s a pain). > > >Thanks, > > >Jeff > > >On Wed, Jan 9, 2019 at 8:12 AM Nathan Hjelm via users ><users@lists.open-mpi.org> wrote: > >If you need to support more attachments you can set the value of that variable >either by setting: > >Environment: > >OMPI_MCA_osc_rdma_max_attach > > >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. > >-Nathan > >> 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 >> MPI_WIN_ATTACH. >> [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 >> _______________________________________________ >> users mailing list >> users@lists.open-mpi.org >> https://lists.open-mpi.org/mailman/listinfo/users > >_______________________________________________ >users mailing list >users@lists.open-mpi.org >https://lists.open-mpi.org/mailman/listinfo/users > >-- > >Jeff Hammond >jeff.scie...@gmail.com >http://jeffhammond.github.io/ >
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