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[Maxim Imakaev <mimakaev@xxxxxxxxx>]

I have experienced the same issue since I started using Ubuntu 8.04.
Often one of the users will run a program which would take a lot of
memory, and this would completely freeze graphics and make all text
terminals very slow. Sometimes I run a code which accidentally allocates
more than my 32GB RAM, and if I don't hit Ctrl+C within 1-2 seconds, it
will never even go through in gnome-terminal. The only solution would be
to  SSH in to the machine and kill the process manually.

In some cases even ssh or console login do not help, and I have to wait
for hours or reboot the machine.

I am surprised that there is no way to save 50-100 megabytes of RAM free
for a root to log in and kill the process; it would be very helpful,
especially when rebooting the computer is not possible.

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

Title:
  System freeze on high memory usage

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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