jecks (slayerproof32), this report is poorly defined, and not root caused as no 
debugging logs have been provided by the original reporter. However, what 
little is known is that the issue for the original reporter was correlated to 
when DMA was disabled in the BIOS, using a now old, and unsupported version of 
Ubuntu. Hence, if you would like your issue root caused and resolved,  you will 
want to file a new report via a terminal:
ubuntu-bug linux

Please feel free to subscribe me to it.

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https://bugs.launchpad.net/bugs/159356

Title:
  System freeze on high memory usage when DMA is disabled

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  I run a batch matlab job server here at my lab, running Dapper 6.06 (for the 
LTS). One of the users has submitted a very memory-consuming job, which 
successfully crashes the server. Upon closer inspection, the crash happens like 
this:
  1. I run matlab with the given file (as an ordinary, unpriveleged user)
  2. RAM usage quickly fills up
  3. Once the RAM meter hits 100%, the system freezes: All SSH connections 
freeze up, and while switching VTs directly on the machine works, no new 
processes run - so one can't log in, or do anything if he is logged in. 
(Sometimes typing doesn't work at all)

  Note that the swap - while 7 gigs of it are available - is never used.
  (The machine has 7 gigs of RAM as well)

  I've tried the same on my Gutsy 32-bit box, and there was no system
  freezeup - matlab simply notified that the system was out of memory.
  However, it did this once memory was 100% in use - and still, swap
  didn't get used at all! (Though it is mounted correctly and shows up
  in "top" and "free").

  So first thing's first - I'd like to eliminate the crash issue. I
  suppose I could switch the server to 32-bit, but I think that would be
  a performance loss, considering that it does a lot of heavy
  computation. There is no reason, however, that this should happen on a
  64-bit machine anyway. Why does it?

  WORKAROUND: Enabling DMA in the BIOS

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