linux-kernel - Re: [RFC Patch V1 22/30] mm, of: Use cpu_to_mem()/numa_mem

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Date:	Mon, 21 Jul 2014 10:52:41 -0700
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	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>,
	Grant Likely <grant.likely@...aro.org>,
	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 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.

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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