[petsc-dev] Fwd: [petsc-users] Unexpected "Out of memory error" with SLEPC

[Karl Rupp]

>    I was thinking of catching the overflow BEFORE it hits the malloc.  For example in DMSetUp_DA_3D() we have the unattractive code
>
> #if !defined(PETSC_USE_64BIT_INDICES)
>    if (((Petsc64bitInt) M)*((Petsc64bitInt) N)*((Petsc64bitInt) P)*((Petsc64bitInt) dof) > (Petsc64bitInt) PETSC_MPI_INT_MAX) SETERRQ3(comm,PETSC_ERR_INT_OVERFLOW,"Mesh of %D by %D by %D (dof) is too large for 32 bit indices",M,N,dof);
> #endif
>
>    Maybe we could introduce some macros like
>
> #if !defined(PETSC_USE_64BIT_INDICES)
> #define  PetscCheckOverflow2(M,N) if (((Petsc64bitInt) M)*((Petsc64bitInt) N) > (Petsc64bitInt) PETSC_MPI_INT_MAX) SETERRQ3(comm,PETSC_ERR_INT_OVERFLOW,”Multiply of %D by %D bis too large for 32 bit indices",M,N;
> #else
> #define  PetscCheckOverflow2(a,b)
> #endif
>
> and then check large products when they are likely to occur.

That's even better in terms of the error message. There are some beasts 
like the following:

src/mat/impls/aij/mpi/mumps/mumps.c:
  ierr = PetscMalloc((2*nz*sizeof(PetscInt)+nz*sizeof(PetscScalar)),
                     &row);CHKERRQ(ierr);

which would require multiiple PetscCheckOverflowX() uses, but I consider 
this acceptable.

Best regards,
Karli