Re: [PATCH v1] memory tier: consolidate the initialization of memory tiers

[Huang, Ying]

Hi, Jack,

Thanks for patch!

"Ho-Ren (Jack) Chuang" <horen.chuang@linux.dev> writes:

> If we simply move the set_node_memory_tier() from memory_tier_init() to
> late_initcall(), it will result in HMAT not registering the
> mt_adistance_algorithm callback function, because set_node_memory_tier()
> is not performed during the memory tiering initialization phase,
> leading to a lack of correct default_dram information.
>
> Therefore, we introduced a nodemask to pass the information of the
> default DRAM nodes. The reason for not choosing to reuse
> default_dram_type->nodes is that it is not clean enough. So in the end,
> we use a __initdata variable, which is a variable that is released once
> initialization is complete, including both CPU and memory nodes for HMAT
> to iterate through.
>
> Besides, since default_dram_type may be checked/used during the
> initialization process of HMAT and drivers, it is better to keep the
> allocation of default_dram_type in memory_tier_init().
>
> Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>

Suggested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
> Hi all,
>
> The current memory tier initialization process is distributed across two
> different functions, memory_tier_init() and memory_tier_late_init(). This
> design is hard to maintain. Thus, this patch is proposed to reduce the
> possible code paths by consolidating different initialization patches into 
> one.
>
> The earlier discussion with Jonathan and Ying is listed here:
> https://lore.kernel.org/lkml/20240405150244.00004b49@Huawei.com/
>
> If we want to put these two initializations together, they must be placed
> together in the later function. Because only at that time, the HMAT 
> information
> will be ready, adist between nodes can be calculated, and memory tiering can 
> be
> established based on the adist. So we position the initialization at
> memory_tier_init() to the memory_tier_late_init() call.
>
> Moreover, it's natural to keep memory_tier initialization in drivers at
> device_initcall() level.
>
> This patchset is based on commits cf93be18fa1b and a72a30af550c:
> [0/2] 
> https://lkml.kernel.org/r/20240405000707.2670063-1-horenchuang@bytedance.com
> [1/2] 
> https://lkml.kernel.org/r/20240405000707.2670063-2-horenchuang@bytedance.com
> [1/2] 
> https://lkml.kernel.org/r/20240405000707.2670063-3-horenchuang@bytedance.com

It appears that you should switch the parts before and after "---".
This is the real patch description, as pointed out by Andrew too.

> Thanks,
> Ho-Ren (Jack) Chuang
>
>  drivers/acpi/numa/hmat.c     |  4 ++-
>  include/linux/memory-tiers.h |  6 ++++
>  mm/memory-tiers.c            | 70 ++++++++++++++++++------------------
>  3 files changed, 44 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
> index 2c8ccc91ebe6..31a77a3324a8 100644
> --- a/drivers/acpi/numa/hmat.c
> +++ b/drivers/acpi/numa/hmat.c
> @@ -939,11 +939,13 @@ static int hmat_set_default_dram_perf(void)
>       int nid, pxm;
>       struct memory_target *target;
>       struct access_coordinate *attrs;
> +     nodemask_t default_dram_nodes;
>  
>       if (!default_dram_type)
>               return -EIO;
>  
> -     for_each_node_mask(nid, default_dram_type->nodes) {
> +     default_dram_nodes = mt_get_default_dram_nodemask();
> +     for_each_node_mask(nid, default_dram_nodes) {

We don't need 'default_dram_type' in the function actually.  It appears
that we can hide it in memory-tiers.c now?

>               pxm = node_to_pxm(nid);
>               target = find_mem_target(pxm);
>               if (!target)
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index 0d70788558f4..1567db7bd40e 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -51,6 +51,7 @@ int mt_perf_to_adistance(struct access_coordinate *perf, 
> int *adist);
>  struct memory_dev_type *mt_find_alloc_memory_type(int adist,
>                                                 struct list_head 
> *memory_types);
>  void mt_put_memory_types(struct list_head *memory_types);
> +nodemask_t mt_get_default_dram_nodemask(void);
>  #ifdef CONFIG_MIGRATION
>  int next_demotion_node(int node);
>  void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
> @@ -149,5 +150,10 @@ static inline struct memory_dev_type 
> *mt_find_alloc_memory_type(int adist,
>  static inline void mt_put_memory_types(struct list_head *memory_types)
>  {
>  }
> +
> +static inline nodemask_t mt_get_default_dram_nodemask(void)
> +{
> +     return NODE_MASK_NONE;
> +}
>  #endif       /* CONFIG_NUMA */
>  #endif  /* _LINUX_MEMORY_TIERS_H */
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 6632102bd5c9..7d4b7f53dd8f 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -43,6 +43,7 @@ static LIST_HEAD(memory_tiers);
>  static LIST_HEAD(default_memory_types);
>  static struct node_memory_type_map node_memory_types[MAX_NUMNODES];
>  struct memory_dev_type *default_dram_type;
> +static nodemask_t default_dram_nodes __initdata = NODE_MASK_NONE;
>  
>  static const struct bus_type memory_tier_subsys = {
>       .name = "memory_tiering",
> @@ -125,6 +126,11 @@ static inline struct memory_tier *to_memory_tier(struct 
> device *device)
>       return container_of(device, struct memory_tier, dev);
>  }
>  
> +nodemask_t __init mt_get_default_dram_nodemask(void)
> +{
> +     return default_dram_nodes;
> +}
> +

Why not just expose 'default_dram_nodes'?

>  static __always_inline nodemask_t get_memtier_nodemask(struct memory_tier 
> *memtier)
>  {
>       nodemask_t nodes = NODE_MASK_NONE;
> @@ -671,27 +677,38 @@ EXPORT_SYMBOL_GPL(mt_put_memory_types);
>  
>  /*
>   * This is invoked via `late_initcall()` to initialize memory tiers for
> - * CPU-less memory nodes after driver initialization, which is
> - * expected to provide `adistance` algorithms.
> + * memory nodes, both with and without CPUs. After the initialization of
> + * firmware and devices, adistance algorithms are expected to be provided.
>   */
>  static int __init memory_tier_late_init(void)
>  {
>       int nid;
> +     struct memory_tier *memtier;
>  
>       guard(mutex)(&memory_tier_lock);
> +     /*
> +      * Look at all the existing and uninitialized N_MEMORY nodes and
> +      * add them to default memory tier or to a tier if we already have
> +      * memory types assigned.
> +      */
>       for_each_node_state(nid, N_MEMORY) {

During the function run, the node may change between N_MEMORY and
!N_MEMORY in theory.  So, it appears necessary to get/put_online_mems()
in the function?

> -             /*
> -              * Some device drivers may have initialized memory tiers
> -              * between `memory_tier_init()` and `memory_tier_late_init()`,
> -              * potentially bringing online memory nodes and
> -              * configuring memory tiers. Exclude them here.
> -              */
> -             if (node_memory_types[nid].memtype)
> -                     continue;
> +             if (!node_state(nid, N_CPU))

Why?  I think that we should "continue" here even if node_state(nid,
N_CPU).

> +                     /*
> +                      * Some device drivers may have initialized
> +                      * memory tiers, potentially bringing memory nodes
> +                      * online and configuring memory tiers.
> +                      * Exclude them here.
> +                      */
> +                     if (node_memory_types[nid].memtype)
> +                             continue;
>  
> -             set_node_memory_tier(nid);
> +             memtier = set_node_memory_tier(nid);
> +             if (IS_ERR(memtier))
> +                     /*
> +                      * Continue with memtiers we are able to setup.
> +                      */
> +                     break;
>       }
> -
>       establish_demotion_targets();
>  
>       return 0;
> @@ -876,7 +893,6 @@ static int __meminit memtier_hotplug_callback(struct 
> notifier_block *self,
>  static int __init memory_tier_init(void)
>  {
>       int ret, node;
> -     struct memory_tier *memtier;
>  
>       ret = subsys_virtual_register(&memory_tier_subsys, NULL);
>       if (ret)
> @@ -887,7 +903,8 @@ static int __init memory_tier_init(void)
>                               GFP_KERNEL);
>       WARN_ON(!node_demotion);
>  #endif
> -     mutex_lock(&memory_tier_lock);
> +
> +     guard(mutex)(&memory_tier_lock);
>       /*
>        * For now we can have 4 faster memory tiers with smaller adistance
>        * than default DRAM tier.
> @@ -898,28 +915,11 @@ static int __init memory_tier_init(void)
>               panic("%s() failed to allocate default DRAM tier\n", __func__);
>  
>       /*
> -      * Look at all the existing N_MEMORY nodes and add them to
> -      * default memory tier or to a tier if we already have memory
> -      * types assigned.
> +      * Record nodes with memory and CPU to set default DRAM performance.
>        */

For one line comments, we can use

        /* Record nodes with memory and CPU to set default DRAM performance. */

> -     for_each_node_state(node, N_MEMORY) {
> -             if (!node_state(node, N_CPU))
> -                     /*
> -                      * Defer memory tier initialization on
> -                      * CPUless numa nodes. These will be initialized
> -                      * after firmware and devices are initialized.
> -                      */
> -                     continue;
> -
> -             memtier = set_node_memory_tier(node);
> -             if (IS_ERR(memtier))
> -                     /*
> -                      * Continue with memtiers we are able to setup
> -                      */
> -                     break;
> -     }
> -     establish_demotion_targets();
> -     mutex_unlock(&memory_tier_lock);
> +     for_each_node_state(node, N_MEMORY)
> +             if (node_state(node, N_CPU))
> +                     node_set(node, default_dram_nodes);

Why not use

        nodes_andnot(default_dram_nodes, node_states[N_MEMORY], 
node_states[N_CPU]);

>       hotplug_memory_notifier(memtier_hotplug_callback, MEMTIER_HOTPLUG_PRI);
>       return 0;

--
Best Regards,
Huang, Ying