Re: [patch 7/8] oom: only kill tasks that share zones with zonelist

[Christoph Lameter <clameter@sgi.com>]

On Thu, 20 Sep 2007, David Rientjes wrote:

> On Thu, 20 Sep 2007, Christoph Lameter wrote:
> 
> > > Setting the CONSTRAINT_MEMORY_POLICY case aside for a moment, what stops 
> > > us from getting rid of taking callback_mutex and simply relying on the 
> > > following to filter for candidate tasks:
> > > 
> > > 	do_each_thread(g, p) {
> > > 		...
> > > 		/*
> > > 		 * Check if it will do any good to kill this task based
> > > 		 * on where it is allowed to allocate.
> > > 		 */
> > > 		if (!nodes_intersects(current->mems_allowed,
> > > 				      p->mems_allowed))
> > > 			continue;
> > > 		...
> > > 	} while_each_thread(g, p);
> > 
> > A global scan over all processes is expensive and may take a long time if 
> > you have a 100000 or so of them.
> > 
> 
> Yeah, I understand that.  Paul and I talked about it a while ago and 
> decided that a per-cpuset file 'oom_kill_asking_task' could be implemented 
> to determine whether the OOM killer would simply kill current or go 
> through select_bad_process() in the CONSTRAINT_CPUSET case to address that 
> problem.  Let me know if that doesn't seem good enough.

There are still allocations that are not constrained to a cpuset. If the 
has an OOM condition on an allocation that is not constrained then the 
above may still cause more troubles.


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