linux-kernel - Re: [PATCH 3/8] mm/numa: Introduce nearest_node

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Message-ID: <Z6-ySS7go_dXl5gM@thinkpad>
Date: Fri, 14 Feb 2025 16:14:49 -0500
From: Yury Norov <yury.norov@...il.com>
To: Andrea Righi <arighi@...dia.com>
Cc: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Joel Fernandes <joel@...lfernandes.org>, Ian May <ianm@...dia.com>,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] mm/numa: Introduce nearest_node_nodemask()

On Fri, Feb 14, 2025 at 08:40:02PM +0100, Andrea Righi wrote:
> Introduce the new helper nearest_node_nodemask() to find the closest
> node in a specified nodemask from a given starting node.
> 
> Returns MAX_NUMNODES if no node is found.
> 
> Suggested-by: Yury Norov [NVIDIA] <yury.norov@...il.com>
> Signed-off-by: Andrea Righi <arighi@...dia.com>

Acked-by: Yury Norov [NVIDIA] <yury.norov@...il.com>

> ---
>  include/linux/numa.h |  7 +++++++
>  mm/mempolicy.c       | 31 +++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/include/linux/numa.h b/include/linux/numa.h
> index 31d8bf8a951a7..e6baaf6051bcf 100644
> --- a/include/linux/numa.h
> +++ b/include/linux/numa.h
> @@ -31,6 +31,8 @@ void __init alloc_offline_node_data(int nid);
>  /* Generic implementation available */
>  int numa_nearest_node(int node, unsigned int state);
>  
> +int nearest_node_nodemask(int node, nodemask_t *mask);
> +
>  #ifndef memory_add_physaddr_to_nid
>  int memory_add_physaddr_to_nid(u64 start);
>  #endif
> @@ -47,6 +49,11 @@ static inline int numa_nearest_node(int node, unsigned int state)
>  	return NUMA_NO_NODE;
>  }
>  
> +static inline int nearest_node_nodemask(int node, nodemask_t *mask)
> +{
> +	return NUMA_NO_NODE;
> +}
> +
>  static inline int memory_add_physaddr_to_nid(u64 start)
>  {
>  	return 0;
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 162407fbf2bc7..488cad280efb3 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -196,6 +196,37 @@ int numa_nearest_node(int node, unsigned int state)
>  }
>  EXPORT_SYMBOL_GPL(numa_nearest_node);
>  
> +/**
> + * nearest_node_nodemask - Find the node in @mask at the nearest distance
> + *			   from @node.
> + *
> + * @node: a valid node ID to start the search from.
> + * @mask: a pointer to a nodemask representing the allowed nodes.
> + *
> + * This function iterates over all nodes in @mask and calculates the
> + * distance from the starting @node, then it returns the node ID that is
> + * the closest to @node, or MAX_NUMNODES if no node is found.
> + *
> + * Note that @node must be a valid node ID usable with node_distance(),
> + * providing an invalid node ID (e.g., NUMA_NO_NODE) may result in crashes
> + * or unexpected behavior.
> + */
> +int nearest_node_nodemask(int node, nodemask_t *mask)
> +{
> +	int dist, n, min_dist = INT_MAX, min_node = MAX_NUMNODES;
> +
> +	for_each_node_mask(n, *mask) {
> +		dist = node_distance(node, n);
> +		if (dist < min_dist) {
> +			min_dist = dist;
> +			min_node = n;
> +		}
> +	}
> +
> +	return min_node;
> +}
> +EXPORT_SYMBOL_GPL(nearest_node_nodemask);
> +
>  struct mempolicy *get_task_policy(struct task_struct *p)
>  {
>  	struct mempolicy *pol = p->mempolicy;
> -- 
> 2.48.1