Tuesday, March 23, 2010

Linux - out-of-memory (L-OOM)

Linux - out-of-memory (L-OOM)

Whilst researching on mobile phones using Linux OS I came across a report on guidelines for creating robust embedded systems (published in 2009). The report's discussion arrived at the topic out-of-memory (OOM) and perceived flaws with Linux overbooking the kernel. The report calls this 'OOM Killer'

The report noted:

"One Linux detractor says this about the feature:

"Linux on the other hand is seriously broken. It will by default answer "yes" to most requests for memory, in the hope that programs ask for more than they actually need. If the hope is fulfilled Linux can run more programs in the same memory, or can run a program that requires more virtual memory than is available. And if not then very bad things happen."

The report then goes on to record this gem of an analogy as to what might happen when Linux over commits.

"One comedian has described this feature of Linux as follows:

"An aircraft company discovered that it was cheaper to fly its planes with less fuel on board. The planes would be lighter and use less fuel and money was saved. On rare occasions however the amount of fuel was insufficient, and the plane would crash. This problem was solved by the engineers of the company by the development of a special OOF (out-of-fuel) mechanism. In emergency cases a passenger was selected and thrown out of the plane. (When necessary, the procedure was repeated.) A large body of theory was developed and many publications were devoted to the problem of properly selecting the victim to be ejected. Should the victim be chosen at random? Or should one choose the heaviest person? Or the oldest? Should passengers pay in order not to be ejected, so that the victim would be the poorest on board? And if for example the heaviest person was chosen, should there be a special exception in case that was the pilot? Should first class passengers be exempted? Now that the OOF mechanism existed, it would be activated every now and then, and eject passengers even when there was no fuel shortage. The engineers are still studying precisely how this malfunction is caused."

No comments: