[petsc-users] petsc4py mpi matrix size

[Lukas Razinkovas]

Thank you very much!

I already checked that its MPIAIJ matrix and for size I use MatGetInfo
routine.
You are right. With matrix of dim 100000x10000 i get sizes:

- serial: 5.603 Mb
- 4 proc.: 7.626 Mb
- 36 proc.: 7.834 Mb

That looks fine to me. Thank you again for such quick response.

I am really impressed with python interface to petsc and slepc.
I think it is missing detailed documentation and that discouraged me to use
it initially,
so I was writing C code and then wrapping it with python. I am still
confused,
how for example to set MUMPS parameters from python code, but that is
different topic.

Lukas



On Fri, Jan 10, 2020 at 5:21 PM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>   Yes, with, for example, MATMPAIJ, the matrix entries are distributed
> among the processes; first verify that you are using a MPI matrix, not Seq,
> since Seq will keep an entire copy on each process.
>
>   But the parallel matrices do come with some overhead for meta data. So
> for small matrices like yours it can seem the memory grows unrealistically.
> Try a much bigger matrix, say 100 times as big and look at the memory usage
> then. You should see that the meta data is now a much smaller percentage of
> the memory usage.
>
>   Also be careful if you use top or other such tools for determining
> memory usage; since malloced() is often not returned to the OS, the can
> indicate much higher memory usage than is really taking place. You can run
> PETSc with -log_view -log_view_memory to get a good idea of where PETSc is
> allocating memory and how much
>
>    Barry
>
>
> > On Jan 10, 2020, at 7:52 AM, Lukas Razinkovas <lukasrazinkovas at gmail.com>
> wrote:
> >
> > Hello,
> >
> > I am trying to use petsc4py and slepc4py for parallel sparse matrix
> diagonalization.
> > However I am a bit confused about matrix size increase when I switch
> from single processor to multiple processors. For example 100 x 100 matrix
> with 298 nonzero elements consumes
> > 8820 bytes of memory (mat.getInfo()["memory"]), however on two processes
> it consumes 20552 bytes of memory  and on four 33528.  My matrix is taken
> from the slepc4py/demo/ex1.py,
> > where nonzero elements are on three diagonals.
> >
> > Why memory usage increases with MPI processes number?
> > I thought that each process stores its own rows and it should stay the
> same. Or some elements are stored globally?
> >
> > Lukas
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20200110/09f00734/attachment.html>