[petsc-users] Call to DMSetMatrixPreallocateSkip not changing allocation behavior

[Matthew Knepley]

On Thu, Dec 14, 2023 at 2:06 PM Fackler, Philip via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> I'm using the following sequence of functions related to the Jacobian
> matrix:
>
> DMDACreate1d(..., &da);
> DMSetFromOptions(da);
> DMSetUp(da);
> DMSetMatType(da, MATAIJKOKKOS);
> DMSetMatrixPreallocateSkip(da, PETSC_TRUE);
> Mat J;
> DMCreateMatrix(da, &J);
> MatSetPreallocationCOO(J, ...);
>
> I recently added the call to DMSetMatrixPreallocateSkip, hoping the
> allocation would be delayed to MatSetPreallocationCOO, and that it would
> require less memory. The documentation
> <https://petsc.org/release/manualpages/DM/DMSetMatrixPreallocateSkip/> says
> that the data structures will not be preallocated.
>

You are completely correct. DMDA is just ignoring this flag. We will fix it.

  Thanks for catching this.

     Matt


> The following data from heaptrack shows that the allocation is still
> happening in the call to DMCreateMatrix.
>
>
> Can someone help me understand this?
>
> Thanks,
>
>
> *Philip Fackler *
> Research Software Engineer, Application Engineering Group
> Advanced Computing Systems Research Section
> Computer Science and Mathematics Division
> *Oak Ridge National Laboratory*
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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