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From: SeongJae Park <sj@kernel.org>
To: Honggyu Kim <honggyu.kim@sk.com>
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	Hyeongtak Ji <hyeongtak.ji@sk.com>
Subject: Re: [RFC PATCH 3/4] mm/memory-tiers: add next_promotion_node to find promotion target
Date: Tue, 16 Jan 2024 12:32:24 -0800
Message-Id: <20240116203224.52877-1-sj@kernel.org>
In-Reply-To: <20240115045253.1775-4-honggyu.kim@sk.com>
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On Mon, 15 Jan 2024 13:52:51 +0900 Honggyu Kim <honggyu.kim@sk.com> wrote:

> From: Hyeongtak Ji <hyeongtak.ji@sk.com>
> 
> This patch adds next_promotion_node that can be used to identify the
> appropriate promotion target based on memory tiers.  When multiple
> promotion target nodes are available, the nearest node is selected based
> on numa distance.
> 
> Signed-off-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
> ---
>  include/linux/memory-tiers.h | 11 +++++++++
>  mm/memory-tiers.c            | 43 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 54 insertions(+)
> 
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index 1e39d27bee41..0788e435fc50 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -50,6 +50,7 @@ int mt_set_default_dram_perf(int nid, struct node_hmem_attrs *perf,
>  int mt_perf_to_adistance(struct node_hmem_attrs *perf, int *adist);
>  #ifdef CONFIG_MIGRATION
>  int next_demotion_node(int node);
> +int next_promotion_node(int node);
>  void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
>  bool node_is_toptier(int node);
>  #else
> @@ -58,6 +59,11 @@ static inline int next_demotion_node(int node)
>  	return NUMA_NO_NODE;
>  }
>  
> +static inline int next_promotion_node(int node)
> +{
> +	return NUMA_NO_NODE;
> +}
> +
>  static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
>  {
>  	*targets = NODE_MASK_NONE;
> @@ -101,6 +107,11 @@ static inline int next_demotion_node(int node)
>  	return NUMA_NO_NODE;
>  }
>  
> +static inline int next_promotion_node(int node)
> +{
> +	return NUMA_NO_NODE;
> +}
> +
>  static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
>  {
>  	*targets = NODE_MASK_NONE;
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 8d5291add2bc..0060ee571cf4 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -335,6 +335,49 @@ int next_demotion_node(int node)
>  	return target;
>  }
>  
> +/*
> + * Select a promotion target that is close to the from node among the given
> + * two nodes.
> + *
> + * TODO: consider other decision policy as node_distance may not be precise.
> + */
> +static int select_promotion_target(int a, int b, int from)
> +{
> +	if (node_distance(from, a) < node_distance(from, b))
> +		return a;
> +	else
> +		return b;
> +}
> +
> +/**
> + * next_promotion_node() - Get the next node in the promotion path
> + * @node: The starting node to lookup the next node
> + *
> + * Return: node id for next memory node in the promotion path hierarchy
> + * from @node; NUMA_NO_NODE if @node is the toptier.
> + */
> +int next_promotion_node(int node)
> +{
> +	int target = NUMA_NO_NODE;
> +	int nid;
> +
> +	if (node_is_toptier(node))
> +		return NUMA_NO_NODE;
> +
> +	rcu_read_lock();
> +	for_each_node_state(nid, N_MEMORY) {
> +		if (node_isset(node, node_demotion[nid].preferred)) {
> +			if (target == NUMA_NO_NODE)
> +				target = nid;
> +			else
> +				target = select_promotion_target(nid, target, node);
> +		}
> +	}
> +	rcu_read_unlock();
> +
> +	return target;
> +}
> +

If this is gonna used by only DAMON and we don't have a concrete plan to making
this used by others, I think implementing this in mm/damon/ might make sense.

>  static void disable_all_demotion_targets(void)
>  {
>  	struct memory_tier *memtier;
> -- 
> 2.34.1