[Bug 159356] Re: When DMA is disabled system freeze on high memory usage

guess I may as well join this party...
I use Xubuntu 16.04 on a few machines, and was initially experiencing this issue for some time...

the machines:

compact:
CPU: Intel Atom D2550 1.86GHz
RAM: 1x2GB DDR3 SO-DIMM
swap: 4GB (OS HDD) + 4GB (Flash Drive)

primary: (no longer operational)
CPU: AMD Athlon II x2 2.7GHz
RAM: 2x2GB DDR3
swap: 2GB (inactive HDD) + 2GB (OS HDD) + 4GB (active HDD)

secondary:
CPU: x86 Intel Pentium4 2.8GHz 1M
RAM: 2x1GB DDR
swap: 8GB (OS HDD)

new-primary:
CPU: x64 Intel Pentium4 3.4GHz +HT
RAM: 4x2GB (only 3504MB used) DDR2
swap: 2GB (SATA-SSD) + 2GB (OS HDD)

on the initial issue, all of these machines (except my primary, or my new primary, which I just got) would freeze when the RAM filled up.
this issue seems to have been fixed some time ago by an update after my primary died, where in the case of that one, it would corrupt the HDD when using swap.
but now after a recent update, the issue is back, and my compact is currently unresponsive.
the issue has also happened on my new primary as well, but not for very long and I was able to close a few browser tabs.

regardless, this needs to be fixed again.

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

Title:
When DMA is disabled 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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