About assigning of arena's to a GPU based MF and CPU based MF respectively.

[chaitanya2596]

Hi,

I'm trying to have a couple of multifabs, in such a way that one of them is allocated on the CPU while the other is allocated on the GPU.
Below is the code which was written,

#######################################################

// Force cpu_mf into the host arena to guarantee host accessibility.
            MFInfo mfi_cpu;
            mfi_cpu.SetArena(The_Arena());
            cpu_mf = new MultiFab(cpu_ba, cpu_dm, ncomp, nghost, mfi_cpu);
            
// If device arena is available use it, otherwise fall back to host arena.
            Arena *dev_arena = The_Device_Arena();
            Arena *use_arena = dev_arena ? dev_arena : The_Arena();

            gpu_mf = new MultiFab(gpu_ba, gpu_dm, ncomp, nghost,
                                  MFInfo().SetArena(use_arena));

#######################################################

But this outputs after assignment that both the arena's are at the same Loc

Arena addresses: The_Arena=0x8d07c80 The_Device_Arena=0x8d07c80

What is that I'm missing here.
Thanks for any help.

[WeiqunZhang]

The_Arena() is GPU device or managed memory and it may be an alias to The_Device_Arena(). https://amrex-codes.github.io/amrex/docs_html/GPU.html#memory-allocation

You can use The_Cpu_Arena() or The_Pinned_Arena() for CPU and The_Arena() for GPU.