[petsc-dev] Lower memory DMDA

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> On Tue, May 7, 2013 at 10:53 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>
>> This thread is complaining about DMDA costing multiple vectors worth
>> of memory.
>>
>> https://groups.google.com/d/msg/claw-dev/JwIjL5e48No/NOizc6i88gkJ
>>
>> We currently set a lot of stuff up eagerly so that it can be accessed
>> using non-collective accessors.  When a Krylov method is used or a
>> matrix is assembled, that stuff is in the noise, but for explicit
>> methods, it can be the limiting factor for problem size.  Should we
>> do something about this?
>>
>
> I would at least like to know what it is, and how the interface would
> have to change. This can't be all scatter memory.

At the very least, it's global-to-local scatter, local-to-local scatter,
and local-to-global mapping (scalar and block).