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

[David Rientjes <rientjes@google.com>]

On Wed, 19 Sep 2007, Christoph Lameter wrote:

> > +		for (vma = mm->mmap; vma; vma = vma->vm_next) {
> > +			unsigned long pfn;
> > +			struct zone *zone;
> > +
> > +			pfn = PFN_DOWN(vma->vm_start);
> > +			zone = page_zone(pfn_to_page(pfn));
> 
> 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);

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().

		David

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