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Date:	Mon, 28 Jul 2014 07:30:40 -0600
From:	Grant Likely <grant.likely@...aro.org>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Rob Herring <robh+dt@...nel.org>,
	Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org,
	linux-hotplug@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [RFC Patch V1 22/30] mm, of: Use cpu_to_mem()/numa_mem_id() to
 support memoryless node

On Mon, 21 Jul 2014 10:52:41 -0700, Nishanth Aravamudan <nacc@...ux.vnet.ibm.com> wrote:
> On 11.07.2014 [15:37:39 +0800], Jiang Liu wrote:
> > When CONFIG_HAVE_MEMORYLESS_NODES is enabled, cpu_to_node()/numa_node_id()
> > may return a node without memory, and later cause system failure/panic
> > when calling kmalloc_node() and friends with returned node id.
> > So use cpu_to_mem()/numa_mem_id() instead to get the nearest node with
> > memory for the/current cpu.
> > 
> > If CONFIG_HAVE_MEMORYLESS_NODES is disabled, cpu_to_mem()/numa_mem_id()
> > is the same as cpu_to_node()/numa_node_id().
> > 
> > Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
> > ---
> >  drivers/of/base.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/of/base.c b/drivers/of/base.c
> > index b9864806e9b8..40d4772973ad 100644
> > --- a/drivers/of/base.c
> > +++ b/drivers/of/base.c
> > @@ -85,7 +85,7 @@ EXPORT_SYMBOL(of_n_size_cells);
> >  #ifdef CONFIG_NUMA
> >  int __weak of_node_to_nid(struct device_node *np)
> >  {
> > -	return numa_node_id();
> > +	return numa_mem_id();
> >  }
> >  #endif
> 
> Um, NAK. of_node_to_nid() returns the NUMA node ID for a given device
> tree node. The default should be the physically local NUMA node, not the
> nearest memory-containing node.

That description doesn't match the code. This patch only changes the
default implementation of of_node_to_nid() which doesn't take the device
node into account *at all* when returning a node ID. Just look at the
diff.

I think this patch is correct, and it doesn't affect the override
versions provided by powerpc and sparc.

g.

> 
> I think the general direction of this patchset is good -- what NUMA
> information do we actually are about at each callsite. But the execution
> is blind and doesn't consider at all what the code is actually doing.
> The changelogs are all identical and don't actually provide any
> information about what errors this (or any) specific patch are
> resolving.
> 
> Thanks,
> Nish
> 

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