MPI_WIN_ALLOCATE_SHARED: memory limited? - fortran

Question

It seems like whenever I am trying to allocate a window around 30-32 Mb I get a segmentation fault?
I am using following routine MPI_WIN_ALLOCATE_SHARED
Does anybody know if there is a limit to how big my window can be? If so, is there a way to compile my code relaxing that limit?
I am using INTEL MPI 19.0.3 and ifort 19.0.3 -
Example written in Fortran. By varying the integer size_ you can see when the segmentation fault occurs. I tested it with size_=10e3 and size_=10e4 the latter caused a segmentation fault
C------
program TEST_STACK
use, INTRINSIC ::ISO_C_BINDING
implicit none
include 'mpif.h'
!--- Parameters (They should not be changed ! )
integer, parameter :: whoisroot = 0 ! - Root always 0 here
!--- General parallel
integer :: whoami ! - My rank
integer :: mpi_nproc ! - no. of procs
integer :: mpierr ! - Error status
integer :: status(MPI_STATUS_SIZE)! - For MPI_RECV
!--- Shared memory stuff
integer :: whoami_shm ! - Local rank in shared memory group
integer :: mpi_shm_nproc ! - No. of procs in Shared memory group
integer :: no_partners ! - No. of partners for share memory
integer :: info_alloc
!--- MPI groups
integer :: world_group ! - All procs across all nodes
integer :: shared_group ! - Only procs that share memory
integer :: MPI_COMM_SHM ! - Shared memory communicators (for those in shared_group)
type(C_PTR) :: ptr_buf
integer(kind = MPI_ADDRESS_KIND) :: size_bytes, lb
integer :: win, size_, disp_unit
call MPI_INIT ( mpierr )
call MPI_COMM_RANK ( MPI_COMM_WORLD, whoami, mpierr )
call MPI_COMM_RANK ( MPI_COMM_WORLD, whoami, mpierr )
call MPI_COMM_SIZE ( MPI_COMM_WORLD, mpi_nproc, mpierr)
call MPI_COMM_SPLIT_TYPE( MPI_COMM_WORLD
& , MPI_COMM_TYPE_SHARED
& , 0
& , MPI_INFO_NULL
& , MPI_COMM_SHM
& , mpierr )
call MPI_COMM_RANK( MPI_COMM_SHM, whoami_shm, mpierr )
call MPI_COMM_SIZE( MPI_COMM_SHM, mpi_shm_nproc, mpierr )
size_ = 10e4! - seg fault
size_bytes = size_ * MPI_REAL
disp_unit = MPI_REAL
size_bytes = size_*disp_unit
call MPI_INFO_CREATE( info_alloc, mpierr )
call MPI_INFO_SET( info_alloc
& , "alloc_shared_noncontig"
& , "true"
& , mpierr )
!
call MPI_WIN_ALLOCATE_SHARED( size_bytes
& , disp_unit
& , info_alloc
& , MPI_COMM_SHM
& , ptr_buf
& , win
& , mpierr )
call MPI_WIN_FREE(win, mpierr)
end program TEST_STACK
I run my code using following command
mpif90 test_stack.f90; mpirun -np 2 ./a.out
This wrapper is linked to my ifort 19.0.3 and Intel MPI library. This has been verified by running
mpif90 -v
and to be very precise my mpif90 is a symbolic link to my mpiifort wrapper. This is made for personal convenience but shouldn't be causing problems I guess?

Answer 1

The manual says that the call to MPI_WIN_ALLOCATE_SHARED looks like this
USE MPI
MPI_WIN_ALLOCATE_SHARED(SIZE, DISP_UNIT, INFO, COMM, BASEPTR, WIN, IERROR)
INTEGER(KIND=MPI_ADDRESS_KIND) SIZE, BASEPTR
INTEGER DISP_UNIT, INFO, COMM, WIN, IERROR
At least the types of disp_unit and baseptr do not match in your program.

Answer 2

I was finally able to diagnose where the error stems from.
In the code I have
disp_unit = MPI_REAL
size_bytes = size_*disp_unit
MPI_REAL is a constant/parameter defined by MPI and is not equal to 4 as I very wrongly expected (4 for 4 bytes for single precision)!. In my version it is set to 1275069468 which most likely refers to an id rather than any sensible number.
Hence, multiplying this number with the size of my array can very quickly exceeds the available memory, but and also the number of digits that can be represented by a byte integer