Re: [PATCH v2 1/1] memory tier: acpi/hmat: create CPUless memory tiers after obtaining HMAT info

[Huang, Ying]

"Ho-Ren (Jack) Chuang" <horenchuang@bytedance.com> writes:

> The current implementation treats emulated memory devices, such as
> CXL1.1 type3 memory, as normal DRAM when they are emulated as normal memory
> (E820_TYPE_RAM). However, these emulated devices have different
> characteristics than traditional DRAM, making it important to
> distinguish them. Thus, we modify the tiered memory initialization process
> to introduce a delay specifically for CPUless NUMA nodes. This delay
> ensures that the memory tier initialization for these nodes is deferred
> until HMAT information is obtained during the boot process. Finally,
> demotion tables are recalculated at the end.
>
> * Abstract common functions into `find_alloc_memory_type()`

We should move kmem_put_memory_types() (renamed to
mt_put_memory_types()?) too.  This can be put in a separate patch.

> Since different memory devices require finding or allocating a memory type,
> these common steps are abstracted into a single function,
> `find_alloc_memory_type()`, enhancing code scalability and conciseness.
>
> * Handle cases where there is no HMAT when creating memory tiers
> There is a scenario where a CPUless node does not provide HMAT information.
> If no HMAT is specified, it falls back to using the default DRAM tier.
>
> * Change adist calculation code to use another new lock, mt_perf_lock.
> In the current implementation, iterating through CPUlist nodes requires
> holding the `memory_tier_lock`. However, `mt_calc_adistance()` will end up
> trying to acquire the same lock, leading to a potential deadlock.
> Therefore, we propose introducing a standalone `mt_perf_lock` to protect
> `default_dram_perf`. This approach not only avoids deadlock but also
> prevents holding a large lock simultaneously.
>
> Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>
> Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
> ---
>  drivers/acpi/numa/hmat.c     | 11 ++++++
>  drivers/dax/kmem.c           | 13 +------
>  include/linux/acpi.h         |  6 ++++
>  include/linux/memory-tiers.h |  8 +++++
>  mm/memory-tiers.c            | 70 +++++++++++++++++++++++++++++++++---
>  5 files changed, 92 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
> index d6b85f0f6082..28812ec2c793 100644
> --- a/drivers/acpi/numa/hmat.c
> +++ b/drivers/acpi/numa/hmat.c
> @@ -38,6 +38,8 @@ static LIST_HEAD(targets);
>  static LIST_HEAD(initiators);
>  static LIST_HEAD(localities);
>  
> +static LIST_HEAD(hmat_memory_types);
> +

HMAT isn't a device driver for some memory devices.  So I don't think we
should manage memory types in HMAT.  Instead, if the memory_type of a
node isn't set by the driver, we should manage it in memory-tier.c as
fallback.

>  static DEFINE_MUTEX(target_lock);
>  
>  /*
> @@ -149,6 +151,12 @@ int acpi_get_genport_coordinates(u32 uid,
>  }
>  EXPORT_SYMBOL_NS_GPL(acpi_get_genport_coordinates, CXL);
>  
> +struct memory_dev_type *hmat_find_alloc_memory_type(int adist)
> +{
> +     return find_alloc_memory_type(adist, &hmat_memory_types);
> +}
> +EXPORT_SYMBOL_GPL(hmat_find_alloc_memory_type);
> +
>  static __init void alloc_memory_initiator(unsigned int cpu_pxm)
>  {
>       struct memory_initiator *initiator;
> @@ -1038,6 +1046,9 @@ static __init int hmat_init(void)
>       if (!hmat_set_default_dram_perf())
>               register_mt_adistance_algorithm(&hmat_adist_nb);
>  
> +     /* Post-create CPUless memory tiers after getting HMAT info */
> +     memory_tier_late_init();
> +

This should be called in memory-tier.c via

late_initcall(memory_tier_late_init);

Then, we don't need hmat to call it.

>       return 0;
>  out_put:
>       hmat_free_structures();
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 42ee360cf4e3..aee17ab59f4f 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -55,21 +55,10 @@ static LIST_HEAD(kmem_memory_types);
>  
>  static struct memory_dev_type *kmem_find_alloc_memory_type(int adist)
>  {
> -     bool found = false;
>       struct memory_dev_type *mtype;
>  
>       mutex_lock(&kmem_memory_type_lock);
> -     list_for_each_entry(mtype, &kmem_memory_types, list) {
> -             if (mtype->adistance == adist) {
> -                     found = true;
> -                     break;
> -             }
> -     }
> -     if (!found) {
> -             mtype = alloc_memory_type(adist);
> -             if (!IS_ERR(mtype))
> -                     list_add(&mtype->list, &kmem_memory_types);
> -     }
> +     mtype = find_alloc_memory_type(adist, &kmem_memory_types);
>       mutex_unlock(&kmem_memory_type_lock);
>  
>       return mtype;
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index b7165e52b3c6..3f927ff01f02 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -434,12 +434,18 @@ int thermal_acpi_critical_trip_temp(struct acpi_device 
> *adev, int *ret_temp);
>  
>  #ifdef CONFIG_ACPI_HMAT
>  int acpi_get_genport_coordinates(u32 uid, struct access_coordinate *coord);
> +struct memory_dev_type *hmat_find_alloc_memory_type(int adist);
>  #else
>  static inline int acpi_get_genport_coordinates(u32 uid,
>                                              struct access_coordinate *coord)
>  {
>       return -EOPNOTSUPP;
>  }
> +
> +static inline struct memory_dev_type *hmat_find_alloc_memory_type(int adist)
> +{
> +     return NULL;
> +}
>  #endif
>  
>  #ifdef CONFIG_ACPI_NUMA
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index 69e781900082..4bc2596c5774 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -48,6 +48,9 @@ int mt_calc_adistance(int node, int *adist);
>  int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
>                            const char *source);
>  int mt_perf_to_adistance(struct access_coordinate *perf, int *adist);
> +struct memory_dev_type *find_alloc_memory_type(int adist,
> +                                                     struct list_head 
> *memory_types);
> +void memory_tier_late_init(void);
>  #ifdef CONFIG_MIGRATION
>  int next_demotion_node(int node);
>  void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
> @@ -136,5 +139,10 @@ static inline int mt_perf_to_adistance(struct 
> access_coordinate *perf, int *adis
>  {
>       return -EIO;
>  }
> +
> +static inline void memory_tier_late_init(void)
> +{
> +
> +}
>  #endif       /* CONFIG_NUMA */
>  #endif  /* _LINUX_MEMORY_TIERS_H */
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 0537664620e5..79f748d60e6f 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -6,6 +6,7 @@
>  #include <linux/memory.h>
>  #include <linux/memory-tiers.h>
>  #include <linux/notifier.h>
> +#include <linux/acpi.h>
>  
>  #include "internal.h"
>  
> @@ -35,6 +36,7 @@ struct node_memory_type_map {
>  };
>  
>  static DEFINE_MUTEX(memory_tier_lock);
> +static DEFINE_MUTEX(mt_perf_lock);

Please add comments about what it protects.  And put it near the data
structure it protects.

>  static LIST_HEAD(memory_tiers);
>  static struct node_memory_type_map node_memory_types[MAX_NUMNODES];
>  struct memory_dev_type *default_dram_type;
> @@ -623,6 +625,58 @@ void clear_node_memory_type(int node, struct 
> memory_dev_type *memtype)
>  }
>  EXPORT_SYMBOL_GPL(clear_node_memory_type);
>  
> +struct memory_dev_type *find_alloc_memory_type(int adist, struct list_head 
> *memory_types)
> +{
> +     bool found = false;
> +     struct memory_dev_type *mtype;
> +
> +     list_for_each_entry(mtype, memory_types, list) {
> +             if (mtype->adistance == adist) {
> +                     found = true;
> +                     break;
> +             }
> +     }
> +     if (!found) {
> +             mtype = alloc_memory_type(adist);
> +             if (!IS_ERR(mtype))
> +                     list_add(&mtype->list, memory_types);
> +     }
> +
> +     return mtype;
> +}
> +EXPORT_SYMBOL_GPL(find_alloc_memory_type);
> +
> +static void memory_tier_late_create(int node)
> +{
> +     struct memory_dev_type *mtype = NULL;
> +     int adist = MEMTIER_ADISTANCE_DRAM;
> +
> +     mt_calc_adistance(node, &adist);
> +     if (adist != MEMTIER_ADISTANCE_DRAM) {

We can manage default_dram_type() via find_alloc_memory_type()
too.

And, if "node_memory_types[node].memtype == NULL", we can call
mt_calc_adistance(node, &adist) and find_alloc_memory_type() in
set_node_memory_tier().  Then, we can cover hotpluged memory node too.

> +             mtype = hmat_find_alloc_memory_type(adist);
> +             if (!IS_ERR(mtype))
> +                     __init_node_memory_type(node, mtype);
> +             else
> +                     pr_err("Failed to allocate a memory type at %s()\n", 
> __func__);
> +     }
> +
> +     set_node_memory_tier(node);
> +}
> +
> +void memory_tier_late_init(void)
> +{
> +     int nid;
> +
> +     mutex_lock(&memory_tier_lock);
> +     for_each_node_state(nid, N_MEMORY)
> +             if (!node_state(nid, N_CPU))

We should exclude "node_memory_types[nid].memtype != NULL".  Some memory
nodes may be onlined by some device drivers and setup memory tiers
already.

> +                     memory_tier_late_create(nid);
> +
> +     establish_demotion_targets();
> +     mutex_unlock(&memory_tier_lock);
> +}
> +EXPORT_SYMBOL_GPL(memory_tier_late_init);
> +
>  static void dump_hmem_attrs(struct access_coordinate *coord, const char 
> *prefix)
>  {
>       pr_info(
> @@ -636,7 +690,7 @@ int mt_set_default_dram_perf(int nid, struct 
> access_coordinate *perf,
>  {
>       int rc = 0;
>  
> -     mutex_lock(&memory_tier_lock);
> +     mutex_lock(&mt_perf_lock);
>       if (default_dram_perf_error) {
>               rc = -EIO;
>               goto out;
> @@ -684,7 +738,7 @@ int mt_set_default_dram_perf(int nid, struct 
> access_coordinate *perf,
>       }
>  
>  out:
> -     mutex_unlock(&memory_tier_lock);
> +     mutex_unlock(&mt_perf_lock);
>       return rc;
>  }
>  
> @@ -700,7 +754,7 @@ int mt_perf_to_adistance(struct access_coordinate *perf, 
> int *adist)
>           perf->read_bandwidth + perf->write_bandwidth == 0)
>               return -EINVAL;
>  
> -     mutex_lock(&memory_tier_lock);
> +     mutex_lock(&mt_perf_lock);
>       /*
>        * The abstract distance of a memory node is in direct proportion to
>        * its memory latency (read + write) and inversely proportional to its
> @@ -713,7 +767,7 @@ int mt_perf_to_adistance(struct access_coordinate *perf, 
> int *adist)
>               (default_dram_perf.read_latency + 
> default_dram_perf.write_latency) *
>               (default_dram_perf.read_bandwidth + 
> default_dram_perf.write_bandwidth) /
>               (perf->read_bandwidth + perf->write_bandwidth);
> -     mutex_unlock(&memory_tier_lock);
> +     mutex_unlock(&mt_perf_lock);
>  
>       return 0;
>  }
> @@ -836,6 +890,14 @@ static int __init memory_tier_init(void)
>        * types assigned.
>        */
>       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 when HMAT information is

HMAT is platform specific, we should avoid to mention it in general code
if possible.

> +                      * available.
> +                      */
> +                     continue;
> +
>               memtier = set_node_memory_tier(node);
>               if (IS_ERR(memtier))
>                       /*

--
Best Regards,
Huang, Ying