Dear All, I would like to understand some details about MPI I/O hints on bg-q and out of memory error while doing collective i/o. Quick Summary : 1. On bg-q I see cb_buffer_size as 16MB when we query on file handle using MPI_File_get_info. An application that we are looking at has code section like: …. MPI_File_set_view( fh, position_to_write, MPI_FLOAT, mappingType, _native_, MPI_INFO_NULL ); max_mb_on_any_rank_using_Kernel_GetMemorySize () => 275 MB MPI_File_write_all( fh, mappingBuffer, .................... MPI_FLOAT, &status); max_mb_on_any_rank_using_Kernel_GetMemorySize () => 373 MB …… Why we see that spike in memory usage? (see Detail section for size information) I have seen “Kernel_GetMemorySize(KERNEL_MEMSIZE_HEAP….)” not returning accurate memory footprint but I am not sure if that is the case here. Darshan screenshot attached shows the access sizes while running on 4 rack. 2. Is romio_cb_alltoall ignored on bg-q? Even if I disable it, I see “automatic” in the output. (I am looking at srcV1R2M4/comm/lib/dev/mpich2/src/mpi/romio/adio/ad_bg/ad_bg_hints.c and see the code section is commented.) More Details : We are debugging an application on MIRA which runs on 1,2,4 racks but fails at 8 racks while dumping a custom checkpoint. These are strong scaling runs and the size of checkpoint remains same (~172GB). 32 ranks per mode. Max memory usage before start of checkpoint (i.e. before single write_all call) for 8 rack is ~ 300 MB. The checkpoint size from each rank is between Kbs to few MBs (as shown by darshan). Once application call checkpoint, we see below error : Out of memory in file /bgsys/source/srcV1R2M2.15270/comm/lib/dev/mpich2/src/mpi/romio/adio/ad_bg/ad_bg_wrcoll.c, line 500 And hence I am confused about behaviour mentioned in question 1. If someone has any insight, it will be great help! Regards, Pramod p.s. Default values of all hints cb_buffer_size, value = 16777216 romio_cb_read, value = enable romio_cb_write, value = enable cb_nodes, value = 8320 (change based on partition size) romio_no_indep_rw, value = false romio_cb_pfr, value = disable romio_cb_fr_types, value = aar romio_cb_fr_alignment, value = 1 romio_cb_ds_threshold, value = 0 romio_cb_alltoall, value = automatic ind_rd_buffer_size, value = 4194304 romio_ds_read, value = automatic romio_ds_write, value = disable _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss
