Re: oom killer and long-waiting processes

From: David Rientjes
Date: Thu Jun 10 2010 - 16:32:44 EST

On Thu, 10 Jun 2010, Ryan Wang wrote:

> Hi all,
> I have one question about oom killer:
> If many processes dealing with network communications,
> but due to bad network traffic, the processes have to wait
> for a very long time. And meanwhile they may consume
> some memeory separately for computation. The number
> of such processes may be large.
> I wonder whether oom killer will kill these processes
> when the system is under high pressure?

The kernel can deal with "high pressure" quite well, but in some cases
such as when all of your RAM or your memory controller is filled with
anonymous memory and cannot be reclaimed, the oom killer may be called to
kill "something". It prefers to kill something that will free a large
amount of memory to avoid having to subsequently kill additional tasks
when it kills something small first.

If there are tasks that you'd either like to protect from the oom killer
or always prefer in oom conditions, you can influence its decision-making
from userspace by tuning /proc/<pid>/oom_adj of the task in question.
Users typically set an oom_adj value of "-17" to completely disable oom
killing of pid (the kernel will even panic if it can't find anything
killable as a result of this!), a value of "-16" to prefer that pid gets
killed last, and a value of "15" to always prefer pid gets killed first.

Lowering a /proc/<pid>/oom_adj value for a pid from its current value (it
inherits its value from the parent, which is usually 0) is only allowed by
root, more specifically, it may only be done by the CAP_SYS_RESOURCE

You can refer to Documentation/filesystems/proc.txt for information on
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