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

[Christoph Lameter <clameter@sgi.com>]

On Wed, 19 Sep 2007, David Rientjes wrote:

> > This seems to assume that all pages in a vma are in the same zone? That is 
> > not the case. On a NUMA system pages may be allocated round robin. Meaning 
> > lots of zones are used that this approach does not catch.
> > 
> 
> 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.

> We shouldn't really be concerned with the changing cpuset states during 
> out_of_memory() since we're only using it as a hint and we're not 
> dereferencing current->cpuset or p->cpuset.  This eliminates the need for 
> cpuset_{lock,unlock}() and cpuset_excl_nodes_overlap().

Yup.

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