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Swap memory usage and free RAM

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Old   January 3, 2013, 11:11
Default Swap memory usage and free RAM
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Hello,
I need some advise.

I am running starccm+ 5.0.6 on a Linux cluster and my cases are running slower than expected.
Looking at the memory usage I can tell that starccm+ has allocated some swap space althought there is plenty of RAM available.

I have set vm.swappiness to 1, but starccm+ continuously tries to page in.

Is there any starccm+ command line option to avoid this "feature"?

Cheers,
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Old   January 3, 2013, 13:15
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What makes you think Star-CCM+ is what is using the swap space? Is 'top' showing Star-CCM+ using more memory than total physical memory being used?

Linux will do things like this that are unintuitive to the user, but actually are the designed behavior. It will use swap space when you don't expect it to. That doesn't mean there is something wrong or your system is running slower than it should.
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Old   January 3, 2013, 13:36
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Hello,
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ SWAP COMMAND
20500 cfd 20 0 2637m 2.0g 33m R 99.6 8.6 528:08.73 62m star-ccm+
20541 cfd 20 0 2296m 1.8g 33m R 98.2 7.5 532:30.48 52m star-ccm+
20536 cfd 20 0 2401m 2.0g 33m R 99.9 8.4 535:54.49 51m star-ccm+
20508 cfd 20 0 2530m 2.1g 33m R 99.6 8.8 536:48.39 49m star-ccm+
20535 cfd 20 0 2202m 1.7g 33m R 99.9 7.4 533:01.86 43m star-ccm+
20410 cfd 20 0 2482m 2.0g 33m R 99.9 8.6 535:18.12 39m star-ccm+
20245 cfd 20 0 2260m 1.9g 34m R 99.9 8.0 534:24.09 37m star-ccm+


When I swapoff -a the number of iteration per hour increases. As soon as I renenable the swap (swapon -a) starccm+ begins to request swap memory and the number of iteration per hour decreases.

This is itop -a -p output
Total DISK READ: 419.41 K/s | Total DISK WRITE: 0.00 B/s
PID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
20541 be/4 cfd 37.52 M 0.00 B 10.11 % 0.47 % star-ccm+ -power test.sim -xmpiversion 2.03.01.00 -mpidriver hp2
20245 be/4 cfd 42.40 M 0.00 B 9.38 % 0.46 % star-ccm+ -power test.sim -xmpiversion 2.03.01.00 -mpidriver hp2
20531 be/4 cfd 1068.00 K 0.00 B 0.07 % 0.45 % star-ccm+ -power test.sim -xmpiversion 2.03.01.00 -mpidriver hp2
20536 be/4 cfd 36.27 M 0.00 B 9.49 % 0.44 % star-ccm+ -power test.sim -xmpiversion 2.03.01.00 -mpidriver hp2
20535 be/4 cfd 46.10 M 0.00 B 10.04 % 0.44 % star-ccm+ -power test.sim -xmpiversion 2.03.01.00 -mpidriver hp2
20410 be/4 cfd 38.08 M 0.00 B 9.97 % 0.43 % star-ccm+ -power test.sim -xmpiversion 2.03.01.00 -mpidriver hp2
20508 be/4 cfd 22.39 M 0.00 B 8.23 % 0.43 % star-ccm+ -power test.sim -xmpiversion 2.03.01.00 -mpidriver hp2

Cheers,
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Old   January 5, 2013, 17:52
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It's not STAR-CCM+ that starts swapping. All the memory management is up to the operating system and hence there can not be any CCM+ option to disable swapping.

Also I wouldn't be concerned since the amount of swap space is just a few megabytes. When your system REALLY needs to swap, you'll notice it since the cpu load will drop to (nearly) 0 since the hard drive is horrible slow and data is not delivered fast enough.
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