Re: [PATCH v3 1/2] memory tier: dax/kmem: 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.
>
> More details:

You have done several stuff in one patch.  So you need "more details".
You may separate them into multiple patches.  One for echo "*" below.
But I have no strong opinion on that.

> * late_initcall(memory_tier_late_init);
> 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. They should be excluded
> in the late init.
>
> * Abstract common functions into `mt_find_alloc_memory_type()`
> Since different memory devices require finding or allocating a memory type,
> these common steps are abstracted into a single function,
> `mt_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.
>
> * Upgrade `set_node_memory_tier` to support additional cases, including
>   default DRAM, late CPUless, and hot-plugged initializations.
> To cover hot-plugged memory nodes, `mt_calc_adistance()` and
> `mt_find_alloc_memory_type()` are moved into `set_node_memory_tier()` to
> handle cases where memtype is not initialized and where HMAT information is
> available.
>
> * Introduce `default_memory_types` for those memory types that are not
>   initialized by device drivers.
> Because late initialized memory and default DRAM memory need to be managed,
> a default memory type is created for storing all memory types that are
> not initialized by device drivers and as a fallback.
>
> Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>
> Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
> ---
>  drivers/dax/kmem.c           | 13 +----
>  include/linux/memory-tiers.h |  7 +++
>  mm/memory-tiers.c            | 94 +++++++++++++++++++++++++++++++++---
>  3 files changed, 95 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 42ee360cf4e3..de1333aa7b3e 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 = mt_find_alloc_memory_type(adist, &kmem_memory_types);
>       mutex_unlock(&kmem_memory_type_lock);
>  
>       return mtype;

It seems that there's some miscommunication about my previous comments
about this.  What I suggested is to create one separate patch, which
moves mt_find_alloc_memory_type() and mt_put_memory_types() into
memory-tiers.c.  And make this patch the first one of the series.

> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index 69e781900082..b2135334ac18 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -48,6 +48,8 @@ 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 *mt_find_alloc_memory_type(int adist,
> +                                                     struct list_head 
> *memory_types);
>  #ifdef CONFIG_MIGRATION
>  int next_demotion_node(int node);
>  void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
> @@ -136,5 +138,10 @@ static inline int mt_perf_to_adistance(struct 
> access_coordinate *perf, int *adis
>  {
>       return -EIO;
>  }
> +
> +struct memory_dev_type *mt_find_alloc_memory_type(int adist, struct 
> list_head *memory_types)
> +{
> +     return NULL;
> +}
>  #endif       /* CONFIG_NUMA */
>  #endif  /* _LINUX_MEMORY_TIERS_H */
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 0537664620e5..d9b96b21b65a 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>

We don't need this anymore.

>  #include "internal.h"
>  
> @@ -36,6 +37,11 @@ struct node_memory_type_map {
>  
>  static DEFINE_MUTEX(memory_tier_lock);
>  static LIST_HEAD(memory_tiers);
> +/*
> + * The list is used to store all memory types that are not created
> + * by a device driver.
> + */
> +static LIST_HEAD(default_memory_types);
>  static struct node_memory_type_map node_memory_types[MAX_NUMNODES];
>  struct memory_dev_type *default_dram_type;
>  
> @@ -505,7 +511,8 @@ static inline void __init_node_memory_type(int node, 
> struct memory_dev_type *mem
>  static struct memory_tier *set_node_memory_tier(int node)
>  {
>       struct memory_tier *memtier;
> -     struct memory_dev_type *memtype;
> +     struct memory_dev_type *memtype, *mtype = NULL;

It seems unnecessary to introduce another variable, just use memtype?

> +     int adist = MEMTIER_ADISTANCE_DRAM;
>       pg_data_t *pgdat = NODE_DATA(node);
>  
>  
> @@ -514,7 +521,18 @@ static struct memory_tier *set_node_memory_tier(int node)
>       if (!node_state(node, N_MEMORY))
>               return ERR_PTR(-EINVAL);
>  
> -     __init_node_memory_type(node, default_dram_type);
> +     mt_calc_adistance(node, &adist);
> +     if (adist != MEMTIER_ADISTANCE_DRAM &&
> +                     node_memory_types[node].memtype == NULL) {
> +             mtype = mt_find_alloc_memory_type(adist, &default_memory_types);
> +             if (IS_ERR(mtype)) {
> +                     mtype = default_dram_type;
> +                     pr_info("Failed to allocate a memory type. Fall 
> back.\n");
> +             }
> +     } else
> +             mtype = default_dram_type;

This can be simplified to

        mt_calc_adistance(node, &adist);
        if (node_memory_types[node].memtype == NULL) {
                mtype = mt_find_alloc_memory_type(adist, &default_memory_types);
                if (IS_ERR(mtype)) {
                        mtype = default_dram_type;
                        pr_info("Failed to allocate a memory type. Fall 
back.\n");
                }
        }

> +     __init_node_memory_type(node, mtype);
>  
>       memtype = node_memory_types[node].memtype;
>       node_set(node, memtype->nodes);
> @@ -623,6 +641,55 @@ void clear_node_memory_type(int node, struct 
> memory_dev_type *memtype)
>  }
>  EXPORT_SYMBOL_GPL(clear_node_memory_type);
>  
> +struct memory_dev_type *mt_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(mt_find_alloc_memory_type);
> +
> +/*
> + * This is invoked via late_initcall() to create
> + * CPUless memory tiers after HMAT info is ready or
> + * when there is no HMAT.

Better to avoid HMAT in general code.  How about something as below?

This is invoked via late_initcall() to initialize memory tiers for
CPU-less memory nodes after drivers initialization.  Which is
expect to provide adistance algorithms.

> + */
> +static int __init 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) &&
> +                     node_memory_types[nid].memtype == NULL)
> +                     /*
> +                      * 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.
> +                      */
> +                     set_node_memory_tier(nid);
> +
> +     establish_demotion_targets();
> +     mutex_unlock(&memory_tier_lock);
> +
> +     return 0;
> +}
> +late_initcall(memory_tier_late_init);
> +
>  static void dump_hmem_attrs(struct access_coordinate *coord, const char 
> *prefix)
>  {
>       pr_info(
> @@ -631,12 +698,16 @@ static void dump_hmem_attrs(struct access_coordinate 
> *coord, const char *prefix)
>               coord->read_bandwidth, coord->write_bandwidth);
>  }
>  
> +/*
> + * The lock is used to protect the default_dram_perf.
> + */
> +static DEFINE_MUTEX(mt_perf_lock);

Miscommunication here too.  Should be moved to near the
"default_dram_perf" definition.  And it protects not only
default_dram_perf.

>  int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
>                            const char *source)
>  {
>       int rc = 0;
>  
> -     mutex_lock(&memory_tier_lock);
> +     mutex_lock(&mt_perf_lock);
>       if (default_dram_perf_error) {
>               rc = -EIO;
>               goto out;
> @@ -684,7 +755,7 @@ 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 +771,7 @@ 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 +784,7 @@ 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;
>  }
> @@ -826,7 +897,8 @@ static int __init memory_tier_init(void)
>        * For now we can have 4 faster memory tiers with smaller adistance
>        * than default DRAM tier.
>        */
> -     default_dram_type = alloc_memory_type(MEMTIER_ADISTANCE_DRAM);
> +     default_dram_type = mt_find_alloc_memory_type(
> +                                     MEMTIER_ADISTANCE_DRAM, 
> &default_memory_types);
>       if (IS_ERR(default_dram_type))
>               panic("%s() failed to allocate default DRAM tier\n", __func__);
>  
> @@ -836,6 +908,14 @@ 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 after firmware and devices 
> are
> +                      * initialized.
> +                      */
> +                     continue;
> +
>               memtier = set_node_memory_tier(node);
>               if (IS_ERR(memtier))
>                       /*

--
Best Regards,
Huang, Ying