[FLASH-USERS] Flash memory usage.

[Brock Palen]

That does help allot,  but being a admin of a system ware a user is  
running flash, I only compiled it and ran the test cases I do not  
understand what its doing.

The max blocks, are blocks a physical property of the model?   
maxblocks is the maximum number of blocks on any one cpus any time  
during the run,  but if block represent physical space in the model,   
and block are distributed among cpus, using more cpus (more nodes to  
get more ram)  and having fewer blocks per cpu would allow us to  
slower maxblocks thus lowering the memory needed by each cpu right?

There is a 95% chance I am completely wrong.  The user is running a  
3d problem.

The formula given to me by Georgi Pavlovski was:

(nvar)x(2*nguard+nxb)x(2*nguard+nyb)x(2*nguard+nzb)x(maxblocks)

So the memory use is proportional to maxblocks.

Brock Palen
Center for Advanced Computing
brockp at umich.edu
(734)936-1985


On Nov 30, 2007, at 9:33 AM, Anshu Dubey wrote:

> The amount of static memory allocated is directly related to the  
> number of
> maxblocks you specify at compile time. Then there is local storage in
> modules that goes on the stack and is usually dependent on the size
> of the individual block. Hdf5_serial IO has relatively large dynamic
> allocation, roughly the size of the local mesh on the processor, and
> paramesh does its own dynamic allocation during communication. This
> allocation depends upon the amount of data that needs to move between
> processors. So the only way allocation is really influenced by  
> spreading
> work out on more nodes is by cutting down the maxblocks  
> proportionately.
> Maxblocks itself is a local quantity, it is the maximum number
> of blocks you anticipate having on any one processor at any time  
> during
> your simulation.
>
> I hope that answers your question, if you need further  
> clarification please
> let me know.
>
> Anshu
>
>
>> How does flash do memory allocation?  If I am running into memory
>> problems but my only option for more memory is to run on more nodes
>> does flash subdivide the amount of memory in use evenly?
>> For example:
>>
>> a model when running on 4 cpus, each process takes 10GB of real  
>> memory.
>>
>> If I run that same model on 8 how close will each process get to 5 gb
>> of use?
>>
>> Brock Palen
>> Center for Advanced Computing
>> brockp at umich.edu
>> (734)936-1985
>>
>>
>
>
>