[petsc-users] GAMG memory consumption

[Matthew Knepley]

On Wed, Nov 24, 2021 at 12:26 PM Karthikeyan Chockalingam - STFC UKRI <
karthikeyan.chockalingam at stfc.ac.uk> wrote:

> Hello,
>
>
>
> I would like to understand why more memory is consumed by -pc_type gamg
> compared to -pc_type mg for the same problem size
>
>
>
> ksp/ksp/tutorial: ./ex45 -da_grid_x 368 -da_grid_x 368 -da_grid_x 368
> -ksp_type cg
>
>
>
> -pc_type mg
>
>
>
> Maximum (over computational time) process memory:        total 1.9399e+10
> max 9.7000e+09 min 9.6992e+09
>
>
>
> -pc_type gamg
>
>
>
> Maximum (over computational time) process memory:        total 4.9671e+10
> max 2.4836e+10 min 2.4835e+10
>
>
>
>
> Am I right in understanding that the memory limiting factor is ‘max
> 2.4836e+10’ as it is the maximum memory used at any given time?
>

Yes, I believe so.

GAMG is using A_C = P^T A P, where P is the prolongation from coarse to
fine, in order to compute the coarse operator A_C, rather than
rediscretization, since it does not have any notion of discretization or
coarse meshes. This takes more memory.

  Thanks,

    Matt


> I have attached the -log_view output of both the preconditioners.
>
>
>
> Best regards,
>
> Karthik.
>
>
>
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-- 
What most experimenters take for granted before they begin their
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https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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