Re: [RFC PATCH 3/4] mm/memory-tiers: add next_promotion_node to find promotion target

SeongJae Park
2024-01-16T20:32:28Z

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