Re: [patch -mm 09/18] oom: add forkbomb penalty to badness heuristic

[David Rientjes <rientjes@google.com>]

On Tue, 1 Jun 2010, David Rientjes wrote:

> On Tue, 1 Jun 2010, KOSAKI Motohiro wrote:
> 
> > > Add a forkbomb penalty for processes that fork an excessively large
> > > number of children to penalize that group of tasks and not others.  A
> > > threshold is configurable from userspace to determine how many first-
> > > generation execve children (those with their own address spaces) a task
> > > may have before it is considered a forkbomb.  This can be tuned by
> > > altering the value in /proc/sys/vm/oom_forkbomb_thres, which defaults to
> > > 1000.
> > > 
> > > When a task has more than 1000 first-generation children with different
> > > address spaces than itself, a penalty of
> > > 
> > > 	(average rss of children) * (# of 1st generation execve children)
> > > 	-----------------------------------------------------------------
> > > 			oom_forkbomb_thres
> > > 
> > > is assessed.  So, for example, using the default oom_forkbomb_thres of
> > > 1000, the penalty is twice the average rss of all its execve children if
> > > there are 2000 such tasks.  A task is considered to count toward the
> > > threshold if its total runtime is less than one second; for 1000 of such
> > > tasks to exist, the parent process must be forking at an extremely high
> > > rate either erroneously or maliciously.
> > > 
> > > Even though a particular task may be designated a forkbomb and selected as
> > > the victim, the oom killer will still kill the 1st generation execve child
> > > with the highest badness() score in its place.  The avoids killing
> > > important servers or system daemons.  When a web server forks a very large
> > > number of threads for client connections, for example, it is much better
> > > to kill one of those threads than to kill the server and make it
> > > unresponsive.
> > > 
> > > [oleg@redhat.com: optimize task_lock when iterating children]
> > > Signed-off-by: David Rientjes <rientjes@google.com>
> > 
> > nack
> > 
> 
> Why?
> 

Still waiting for an answer to this, KOSAKI.

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