[petsc-dev] [petsc-users] MatPreallocatorPreallocate segfault with PETSC 3.16

Patrick Sanan patrick.sanan at gmail.com
Fri Feb 4 05:03:03 CST 2022

So, seems like a fix we should make at this point is to make
MatPreallocator explicitly single use, throwing an error if
MatPreallocatorPreallocate is called a second time. (Still open for further
debate as to what to do in general but this quick patch to release to
replace the crash with an error message seems justified in any case).

Am Fr., 4. Feb. 2022 um 02:02 Uhr schrieb Jed Brown <jed at jedbrown.org>:

> MatPreallocator stores "the nonzero structure" in a hash table so it can
> be easily updated. A normal Mat stores it in a compressed (CSR) format that
> is expensive to update.
> Marius Buerkle <mbuerkle at web.de> writes:
> > Ok. I did not know that. I was under the impression that MatPreallocator
> does actually not allocate the nonzeros and just stores the nonzero
> structure. But if this is not the case then of course I just duplicate the
> matrix.
> >
> > Thanks for the feedback.
> >
> >> Gesendet: Donnerstag, den 03.02.2022 um 03:09 Uhr
> >> Von: "Jed Brown" <jed at jedbrown.org>
> >> An: "Marius Buerkle" <mbuerkle at web.de>, "Patrick Sanan" <
> patrick.sanan at gmail.com>
> >> Cc: "PETSc users list" <petsc-users at mcs.anl.gov>, petsc-dev <
> petsc-dev at mcs.anl.gov>
> >> Betreff: Re: Aw: Re: [petsc-dev] [petsc-users]
> MatPreallocatorPreallocate segfault with PETSC 3.16
> >>
> >> Marius Buerkle <mbuerkle at web.de> writes:
> >>
> >> > Thanks for they reply. Yes the example works, this is how I was doing
> it before. But the matrix is rather big and i need a matrix with the same
> structure at various points in my code. So it was convenient to create the
> matrix with preallocate, destroy it after using it to free the memory and
> creating it again later with the same preallocate.
> >> > Anyway it works with MatDuplicate for now.
> >>
> >> I think it should take *less* memory to destroy the preallocator and
> duplicate the actual matrix than to destroy the matrix and persist the
> preallocator. If that is not the case (or close enough), we can make it so.
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