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I have a machine running Ubuntu on Amazon EC2. The machine has a 43 Gb root drive and 30 Gb of RAM. I am running a processor and memory intensive process and I've noticed that it sometimes stalls for no apparent reason. I'm looking at the system usage via the htop program. I've included a screenshot below.

Does it make sense that the VIRT column adds up to more than the physical drive space of the system? My understanding is that is virtual memory usage. Essentially I'm trying to understand whether my process is freezing because it's running out of resources, and which resources it's running out of.

System usage. Virtual memory is exceeding the root drive space.

  • RSS is the physical memory used, VIRT is the entire address space (swap+RSS) – Bratchley May 27 '14 at 20:13
  • RSS, do you mean RES? The sum of the RES column exceeds the total memory the system has - 30gb – gallamine May 27 '14 at 20:16
  • Yeah RSS is the same as RES. Since the VIRT and RES for several of those processes match up, I'd see if those PID's are threads of the same process, in which case they'll share the same memory and so should only be counted once. – Bratchley May 27 '14 at 20:28
  • The processes I'm talking about are the 10.1GB for VIRT and 9121MB for RSS. – Bratchley May 27 '14 at 20:28
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    I'm assuming you checked and they are? If you aren't sure, you can try going go into setup>display options and tell it to display threads in a different color. – Bratchley May 27 '14 at 20:41
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This is normal; it's because Linux has overcommit (overcommit.ratio) and VIRT is also shared memory between processes that use the same shared objects.

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