[petsc-users] Questions about memory usage in Petsc

[neil liu]

Thanks a lot for this advice. Will do.

On Wed, Dec 3, 2025 at 4:18 PM Barry Smith <bsmith at petsc.dev> wrote:

>
>    Unix/Linux has never had a good API for tracking process memory usage. PetscMemoryGetCurrentUsage()
> gets what it can from the OS, but the exact number should not be considered
> a true measure of process memory usage at that point in time.  Jumps up and
> down are not accurate measures of changes in memory usage.
>
>   PetscMallocGetCurrentUsage() and the number from MUMPS are (assuming no
> bugs in our code and MUMPS counting space) accurate values of memory usage.
> You should use these to see how memory usage is scaling with your problem
> size.
>
>   Barry
>
>
> On Dec 3, 2025, at 4:00 PM, neil liu <liufield at gmail.com> wrote:
>
> Dear users and developers,
>
> I am recently running a large system from Nedelec element, 14 million dofs
> (complex number).
> A little confused about the memory there. Then I tried a small system
> (34,000 dofs) to see the memory usage. It was solved with MUMPS with 1
> rank.
> Then I used  PetscMemoryGetCurrentUsage() to show the memory used there.
> The pseudocode is
> PetscMemoryGetCurrentUsage (*Memory 1:* 64.237M)
> KSPset
> KSPsolve  (INFOG(18) (size of all MUMPS internal data allocated during
> factorization: value on the most memory consuming processor): *Memory 2:*  408
> MB)
> PetscMemoryGetCurrentUsage (*Memory 3: *54.307M)
>
> [0] Maximum memory PetscMalloc()ed 49.45MB maximum size of entire process
> 424MB (*Memory 4:* 54.307M)
> The following is my understanding, please correct me if I am wrong,
> It seems the difference between Memory 1 and 3 is approximately the size
> of 30 Krylov vectors (complex).
> It seems Memory 4 is not the summation of Memory 2 and 3; but on the same
> order of magnitude. It is a little confusing here.
>
> Thanks,
> Xiaodong
>
>
>
>
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