[Dune] Memmory consumption for parallel unstructured grids

[Christian Engwer]

Dear Paul,

first of all sorry for the late reply, you email got lost in a bunch o
spam mails.

The problem you are describing is not immediate to me, but in general
you mesh is arther small so that the relative number of shared cells
is rather large. As a consequence you need more memory.

Perhaps you can give some numbers / a table:
 - how does the # of ghost cells increase with growing processes
 - how many cells are in your seq. mesh
 - with how many processes did you test with

...

In general such a behaviour is not totally surprising, but I don't
want to claim that there is not also a possible memory management
problem.

Best
Christian

> I am working with a parallel unstructured grid in my Dune project. I
> currently have the following behaviour, that I cannot explain.
> 
> When I increase the number of processes the overall memory consumption
> increases significantly depending on the number of processes by a factor 2
> and more. Especially the process with rank 0 has a very high memory demand.
> 
> I see that there is some overhead when increasing the number of processes
> but this seems to me a lot and more than the number of ghost cells would
> justify.
> 
> This behaviour is appears in UGGrid and in ALUGrid.
> 
>  
> 
> I have created a small example script, which is attached together with an
> example mesh file. 
> 
> My questions are:
> 
> Is this a normal behaviour? If so can you please give a short explanation
> why this is the case?
> 
> If this is not expected, have I done something wrong when handling the grid?
> 
> And do you know a way to avoid this behaviour?
> 
>  
> 
> Best regards and thanks a lot in advance
> 
> Paul Maidl