Re: [RFC PATCH 2/3] topology: support node_numa_mem() for determining the fallback node

[David Rientjes <rientjes@google.com>]

On Thu, 6 Feb 2014, Joonsoo Kim wrote:

> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 

I may be misunderstanding this patch and there's no help because there's 
no changelog.

> diff --git a/include/linux/topology.h b/include/linux/topology.h
> index 12ae6ce..a6d5438 100644
> --- a/include/linux/topology.h
> +++ b/include/linux/topology.h
> @@ -233,11 +233,20 @@ static inline int numa_node_id(void)
>   * Use the accessor functions set_numa_mem(), numa_mem_id() and cpu_to_mem().
>   */
>  DECLARE_PER_CPU(int, _numa_mem_);
> +int _node_numa_mem_[MAX_NUMNODES];
>  
>  #ifndef set_numa_mem
>  static inline void set_numa_mem(int node)
>  {
>  	this_cpu_write(_numa_mem_, node);
> +	_node_numa_mem_[numa_node_id()] = node;
> +}
> +#endif
> +
> +#ifndef get_numa_mem
> +static inline int get_numa_mem(int node)
> +{
> +	return _node_numa_mem_[node];
>  }
>  #endif
>  
> @@ -260,6 +269,7 @@ static inline int cpu_to_mem(int cpu)
>  static inline void set_cpu_numa_mem(int cpu, int node)
>  {
>  	per_cpu(_numa_mem_, cpu) = node;
> +	_node_numa_mem_[numa_node_id()] = node;

The intention seems to be that _node_numa_mem_[X] for a node X will return 
a node Y with memory that has the nearest distance?  In other words, 
caching the value returned by local_memory_node(X)?

That doesn't seem to be what it's doing since numa_node_id() is the node 
of the cpu that current is running on so this ends up getting initialized 
to whatever local_memory_node(cpu_to_node(cpu)) is for the last bit set in 
cpu_possible_mask.

>  }
>  #endif
>  
> @@ -273,6 +283,13 @@ static inline int numa_mem_id(void)
>  }
>  #endif
>  
> +#ifndef get_numa_mem
> +static inline int get_numa_mem(int node)
> +{
> +	return node;
> +}
> +#endif
> +
>  #ifndef cpu_to_mem
>  static inline int cpu_to_mem(int cpu)
>  {

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