CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM

solved issue of running out of virtual memory crashes

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By mihaipruna

Reply
 
LinkBack Thread Tools Display Modes
Old   April 13, 2012, 16:00
Default solved issue of running out of virtual memory crashes
  #1
Senior Member
 
Mihai Pruna
Join Date: Apr 2010
Location: Boston
Posts: 190
Blog Entries: 1
Rep Power: 7
mihaipruna is on a distinguished road
I looked for this particular issue and nobody seems to have answered it.
The dreaded message: "This does not necessarily mean you have run out of virtual memory"...
Basically my SHM mesher would crash for large numbers of cells.
This seems to have fixed it:

On Ubuntu, Use this tutorial to increase the size of the swap partition or add a new one

https://help.ubuntu.com/community/SwapFaq
wyldckat likes this.
__________________
Mihai Pruna's Bio
mihaipruna is offline   Reply With Quote

Old   April 17, 2012, 07:22
Default
  #2
Senior Member
 
Join Date: Aug 2010
Location: Groningen, The Netherlands
Posts: 216
Rep Power: 9
colinB is on a distinguished road
Hi mihaipruna,

using swap partitions is basically assigning a part of the hard-drive as
RAM which the computer also may use to deal with big files.

But this is not an optimal solution to deal with the problem, since
the calculations (both mesh creation and solving) are slowed down
significantly.
This is due to the extra 'way' of communicating.
Without swap just RAM and Processor have to communicate and these
two are built that way to handle the amount of data the RAM can store
within a short time span.
Now also introducing a swap partition to increase the RAM capacities
this additional way of communication , which is actually not
meant to do so, but for storing (big) files permanently, slows down the
process, for the data has to be hauled forth and back from there as well.

I would be interested if the solver is actually not complaining about such a
big mesh or if he is also using the swap partition without further notes?

Another note:

In a different thread where you posted the link to this thread
I mentioned a rule of thumb for mesh creation with 1M cells per GB RAM.
This rule of thumb should be extended:
Don't use more than 2 GB of RAM per processor.
So the number of processors is somehow also limiting your mesh size.

In reality this means with a quadcore machine I'm limited to 8M cells as
long as 8 GB RAM are provided.

With these guidelines I got pretty good results without hitting any
hardware limits.They are however just proven for PCs not for clusters
or other 'super computers'

best regards

Colin
colinB is offline   Reply With Quote

Old   April 17, 2012, 09:45
Default
  #3
Senior Member
 
Mihai Pruna
Join Date: Apr 2010
Location: Boston
Posts: 190
Blog Entries: 1
Rep Power: 7
mihaipruna is on a distinguished road
I'm not sure how OpenFOAM handles multiple processors, do you have to tell it to run in parallel mode?
__________________
Mihai Pruna's Bio
mihaipruna is offline   Reply With Quote

Old   April 17, 2012, 15:45
Default
  #4
Super Moderator
 
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 8,301
Blog Entries: 34
Rep Power: 84
wyldckat is just really nicewyldckat is just really nicewyldckat is just really nicewyldckat is just really nice
Greetings to all!

@Mihai:
Quote:
Originally Posted by mihaipruna View Post
I'm not sure how OpenFOAM handles multiple processors, do you have to tell it to run in parallel mode?
See the tutorial "./incompressible/simpleFoam/turbineSiting" as an example for running snappyHexMesh in parallel as well as running simpleFoam in parallel.
The "damBreak" tutorial (the 2nd one, I think) in the OpenFOAM User Guide explains the first steps into running OpenFOAM applications in parallel.

Best regards,
Bruno
wyldckat is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
another issue about HPC cluster for running cfx, hepl PLZ. happy CFX 4 March 5, 2012 00:58
parallel running issue xiaokang Fluent UDF and Scheme Programming 0 January 18, 2012 18:42
Stability issue while running buoyantFoam fandall OpenFOAM Running, Solving & CFD 13 May 9, 2011 11:36
Issue with running in parallel on multiple nodes daveatstyacht OpenFOAM 7 August 31, 2010 17:16
Memory issue - Suse 10 - Opterons Andy R FLUENT 1 June 23, 2008 14:44


All times are GMT -4. The time now is 06:29.