Re: [PATCH 1/2] mm: refactor find_next_best_node to find_next_best_node_in

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 9/2/26 23:58, Gregory Price wrote:
> find_next_best_node() picks the next-closest node for a fallback list
> from the full N_MEMORY set. Refactor it into find_next_best_node_in(),
> which takes an explicit candidates nodemask.
> 
> This enables building fallback lists with non-N_MEMORY candidates.
> 
> No functional change: every caller still selects from N_MEMORY.
> 
> Signed-off-by: Gregory Price <gourry@gourry.net>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Nit:

> ---
>  mm/internal.h     |  6 ++++--
>  mm/memory-tiers.c |  7 ++++---
>  mm/page_alloc.c   | 13 ++++++++-----
>  3 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index e16f1250b25c8..18d041ff5c52c 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1130,7 +1130,8 @@ extern int node_reclaim_mode;
>  
>  extern unsigned long node_reclaim(struct pglist_data *pgdat,
>  				  gfp_t gfp_mask, unsigned int order);
> -extern int find_next_best_node(int node, nodemask_t *used_node_mask);
> +extern int find_next_best_node_in(int node, nodemask_t *used_node_mask,
> +				  const nodemask_t *candidates);

Drop the extern while touching a line.

>  #else
>  #define node_reclaim_mode 0
>  
> @@ -1139,7 +1140,8 @@ static inline unsigned long node_reclaim(struct pglist_data *pgdat,
>  {
>  	return 0;
>  }
> -static inline int find_next_best_node(int node, nodemask_t *used_node_mask)
> +static inline int find_next_best_node_in(int node, nodemask_t *used_node_mask,
> +					 const nodemask_t *candidates)
>  {
>  	return NUMA_NO_NODE;
>  }
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 54851d8a195b0..25e121851b586 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -370,7 +370,7 @@ int next_demotion_node(int node, const nodemask_t *allowed_mask)
>  	 * closest demotion target.
>  	 */
>  	nodes_complement(mask, *allowed_mask);
> -	return find_next_best_node(node, &mask);
> +	return find_next_best_node_in(node, &mask, &node_states[N_MEMORY]);
>  }
>  
>  static void disable_all_demotion_targets(void)
> @@ -450,7 +450,7 @@ static void establish_demotion_targets(void)
>  		memtier = list_next_entry(memtier, list);
>  		tier_nodes = get_memtier_nodemask(memtier);
>  		/*
> -		 * find_next_best_node, use 'used' nodemask as a skip list.
> +		 * find_next_best_node_in, use 'used' nodemask as a skip list.
>  		 * Add all memory nodes except the selected memory tier
>  		 * nodelist to skip list so that we find the best node from the
>  		 * memtier nodelist.
> @@ -463,7 +463,8 @@ static void establish_demotion_targets(void)
>  		 * in the preferred mask when allocating pages during demotion.
>  		 */
>  		do {
> -			target = find_next_best_node(node, &tier_nodes);
> +			target = find_next_best_node_in(node, &tier_nodes,
> +							&node_states[N_MEMORY]);
>  			if (target == NUMA_NO_NODE)
>  				break;
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c4dc61ec663ee..4dde1cbe2fd43 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5779,9 +5779,10 @@ static int numa_zonelist_order_handler(const struct ctl_table *table, int write,
>  static int node_load[MAX_NUMNODES];
>  
>  /**
> - * find_next_best_node - find the next node that should appear in a given node's fallback list
> + * find_next_best_node_in - find the next node that should appear in a given node's fallback list
>   * @node: node whose fallback list we're appending
>   * @used_node_mask: nodemask_t of already used nodes
> + * @candidates: nodemask_t of nodes eligible for selection
>   *
>   * We use a number of factors to determine which is the next node that should
>   * appear on a given node's fallback list.  The node should not have appeared
> @@ -5793,7 +5794,8 @@ static int node_load[MAX_NUMNODES];
>   *
>   * Return: node id of the found node or %NUMA_NO_NODE if no node is found.
>   */
> -int find_next_best_node(int node, nodemask_t *used_node_mask)
> +int find_next_best_node_in(int node, nodemask_t *used_node_mask,
> +			   const nodemask_t *candidates)
>  {
>  	int n, val;
>  	int min_val = INT_MAX;
> @@ -5803,12 +5805,12 @@ int find_next_best_node(int node, nodemask_t *used_node_mask)
>  	 * Use the local node if we haven't already, but for memoryless local
>  	 * node, we should skip it and fall back to other nodes.
>  	 */
> -	if (!node_isset(node, *used_node_mask) && node_state(node, N_MEMORY)) {
> +	if (!node_isset(node, *used_node_mask) && node_isset(node, *candidates)) {
>  		node_set(node, *used_node_mask);
>  		return node;
>  	}
>  
> -	for_each_node_state(n, N_MEMORY) {
> +	for_each_node_mask(n, *candidates) {
>  
>  		/* Don't want a node to appear more than once */
>  		if (node_isset(n, *used_node_mask))
> @@ -5893,7 +5895,8 @@ static void build_zonelists(pg_data_t *pgdat)
>  	prev_node = local_node;
>  
>  	memset(node_order, 0, sizeof(node_order));
> -	while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {
> +	while ((node = find_next_best_node_in(local_node, &used_mask,
> +					      &node_states[N_MEMORY])) >= 0) {
>  		/*
>  		 * We don't want to pressure a particular node.
>  		 * So adding penalty to the first node in same