Segmentation error when initializing a large array

Accelerated Computing HPC Compilers Legacy PGI Compilers
1

Hi all,

I encounter with a problem when I am trying to initialize a large size zero arrays (x(2, 2800, 1600000)). I make it an allocatable array but still the segmentation fault message appears.

Here is my code:

program test
 integer(kind=1), allocatable :: x(:, :, :)
 allocate(x(2, 2800, 1600000))

 x = 0_1

end program

I’ve tried ulimit -s unlimited but it didn’t work. I am working on a workstation and I suppose it should have larger memory than 8.34GB. Could anyone help with this?

Thanks,
Zejin

2

Hi Zejin,

For large dynamically allocated arrays (>2GB), you need to compile with the “-Mlarge_arrays” or “-mcmodel=medium” options. Since there’s extra overhead with managing larger arrays, we don’t enable this support by default.

Hope this helps,
Mat

3

Hi Mat,

Thanks for replying. This exactly solves my problem!
Thank you very much.

Best,
Zejin

4

FYI - Mlarge_arrays switch tells the compiler to calculate its
array-index-to-byte-offset math using 64-bit integers instead of 32-bit.
The offset for x(1,1500,1400000) would be
115001400000*4(bytes per array element) which could go beyond
32-bit limits.

-mcmodel=medium
means to convert to an object file format that accepts large statically
allocated arrays. It usually runs slower, so allocate the big arrays
dynamically and avoid -mcmodel=medium, but use -Mlarge_arrays
only.

dave