[v4,2/2] memory tier: create CPUless memory tiers after obtaining HMAT info

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.

* 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.

* 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.

* Introduce another new lock `default_dram_perf_lock` for adist calculation
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 `default_dram_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>
---
 mm/memory-tiers.c | 73 ++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 63 insertions(+), 10 deletions(-)

"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.
>
> * 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.
>
> * 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.
>
> * Introduce another new lock `default_dram_perf_lock` for adist calculation
> 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 `default_dram_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>
> ---
>  mm/memory-tiers.c | 73 ++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 63 insertions(+), 10 deletions(-)
>
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 974af10cfdd8..9396330fa162 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -36,6 +36,11 @@ 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;
>  
> @@ -108,6 +113,7 @@ static struct demotion_nodes *node_demotion __read_mostly;
>  
>  static BLOCKING_NOTIFIER_HEAD(mt_adistance_algorithms);
>
> +static DEFINE_MUTEX(default_dram_perf_lock);

Better to add comments about what is protected by this lock.

>  static bool default_dram_perf_error;
>  static struct access_coordinate default_dram_perf;
>  static int default_dram_perf_ref_nid = NUMA_NO_NODE;
> @@ -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 *mtype;

mtype may be referenced without initialization now below.

> +	int adist = MEMTIER_ADISTANCE_DRAM;
>  	pg_data_t *pgdat = NODE_DATA(node);
>  
>  
> @@ -514,11 +521,20 @@ 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 (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");
> +		}
> +	}
>  
> -	memtype = node_memory_types[node].memtype;
> -	node_set(node, memtype->nodes);
> -	memtier = find_create_memory_tier(memtype);
> +	__init_node_memory_type(node, mtype);
> +
> +	mtype = node_memory_types[node].memtype;
> +	node_set(node, mtype->nodes);
> +	memtier = find_create_memory_tier(mtype);
>  	if (!IS_ERR(memtier))
>  		rcu_assign_pointer(pgdat->memtier, memtier);
>  	return memtier;
> @@ -655,6 +671,34 @@ void mt_put_memory_types(struct list_head *memory_types)
>  }
>  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.
> + */
> +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(
> @@ -668,7 +712,7 @@ int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
>  {
>  	int rc = 0;
>  
> -	mutex_lock(&memory_tier_lock);
> +	mutex_lock(&default_dram_perf_lock);
>  	if (default_dram_perf_error) {
>  		rc = -EIO;
>  		goto out;
> @@ -716,7 +760,7 @@ int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
>  	}
>  
>  out:
> -	mutex_unlock(&memory_tier_lock);
> +	mutex_unlock(&default_dram_perf_lock);
>  	return rc;
>  }
>  
> @@ -732,7 +776,7 @@ 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(&default_dram_perf_lock);
>  	/*
>  	 * The abstract distance of a memory node is in direct proportion to
>  	 * its memory latency (read + write) and inversely proportional to its
> @@ -745,7 +789,7 @@ 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(&default_dram_perf_lock);
>  
>  	return 0;
>  }
> @@ -858,7 +902,8 @@ 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__);
>  
> @@ -868,6 +913,14 @@ 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

On Fri, Mar 22, 2024 at 1:41 AM Huang, Ying <ying.huang@intel.com> wrote:
>
> "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.
> >
> > * 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.
> >
> > * 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.
> >
> > * Introduce another new lock `default_dram_perf_lock` for adist calculation
> > 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 `default_dram_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>
> > ---
> >  mm/memory-tiers.c | 73 ++++++++++++++++++++++++++++++++++++++++-------
> >  1 file changed, 63 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> > index 974af10cfdd8..9396330fa162 100644
> > --- a/mm/memory-tiers.c
> > +++ b/mm/memory-tiers.c
> > @@ -36,6 +36,11 @@ 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;
> >
> > @@ -108,6 +113,7 @@ static struct demotion_nodes *node_demotion __read_mostly;
> >
> >  static BLOCKING_NOTIFIER_HEAD(mt_adistance_algorithms);
> >
> > +static DEFINE_MUTEX(default_dram_perf_lock);
>
> Better to add comments about what is protected by this lock.
>

Thank you. I will add a comment like this:
+ /* The lock is used to protect `default_dram_perf*` info and nid. */
+static DEFINE_MUTEX(default_dram_perf_lock);

I also found an error path was not handled and
found the lock could be put closer to what it protects.
I will have them fixed in V5.

> >  static bool default_dram_perf_error;
> >  static struct access_coordinate default_dram_perf;
> >  static int default_dram_perf_ref_nid = NUMA_NO_NODE;
> > @@ -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 *mtype;
>
> mtype may be referenced without initialization now below.
>

Good catch! Thank you.

Please check below.
I may found a potential NULL pointer dereference.

> > +     int adist = MEMTIER_ADISTANCE_DRAM;
> >       pg_data_t *pgdat = NODE_DATA(node);
> >
> >
> > @@ -514,11 +521,20 @@ 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 (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");
> > +             }
> > +     }
> >
> > -     memtype = node_memory_types[node].memtype;
> > -     node_set(node, memtype->nodes);
> > -     memtier = find_create_memory_tier(memtype);
> > +     __init_node_memory_type(node, mtype);
> > +
> > +     mtype = node_memory_types[node].memtype;
> > +     node_set(node, mtype->nodes);

If the `mtype` could be NULL, would there be a potential
NULL pointer dereference. Do you have a preferred idea
to fix this if needed?

> > +     memtier = find_create_memory_tier(mtype);
> >       if (!IS_ERR(memtier))
> >               rcu_assign_pointer(pgdat->memtier, memtier);
> >       return memtier;
> > @@ -655,6 +671,34 @@ void mt_put_memory_types(struct list_head *memory_types)
> >  }
> >  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.
> > + */
> > +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(
> > @@ -668,7 +712,7 @@ int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
> >  {
> >       int rc = 0;
> >
> > -     mutex_lock(&memory_tier_lock);
> > +     mutex_lock(&default_dram_perf_lock);
> >       if (default_dram_perf_error) {
> >               rc = -EIO;
> >               goto out;
> > @@ -716,7 +760,7 @@ int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
> >       }
> >
> >  out:
> > -     mutex_unlock(&memory_tier_lock);
> > +     mutex_unlock(&default_dram_perf_lock);
> >       return rc;
> >  }
> >
> > @@ -732,7 +776,7 @@ 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(&default_dram_perf_lock);
> >       /*
> >        * The abstract distance of a memory node is in direct proportion to
> >        * its memory latency (read + write) and inversely proportional to its
> > @@ -745,7 +789,7 @@ 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(&default_dram_perf_lock);
> >
> >       return 0;
> >  }
> > @@ -858,7 +902,8 @@ 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__);
> >
> > @@ -868,6 +913,14 @@ 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

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

> On Fri, Mar 22, 2024 at 1:41 AM Huang, Ying <ying.huang@intel.com> wrote:
>>
>> "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.
>> >
>> > * 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.
>> >
>> > * 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.
>> >
>> > * Introduce another new lock `default_dram_perf_lock` for adist calculation
>> > 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 `default_dram_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>
>> > ---
>> >  mm/memory-tiers.c | 73 ++++++++++++++++++++++++++++++++++++++++-------
>> >  1 file changed, 63 insertions(+), 10 deletions(-)
>> >
>> > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>> > index 974af10cfdd8..9396330fa162 100644
>> > --- a/mm/memory-tiers.c
>> > +++ b/mm/memory-tiers.c
>> > @@ -36,6 +36,11 @@ 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;
>> >
>> > @@ -108,6 +113,7 @@ static struct demotion_nodes *node_demotion __read_mostly;
>> >
>> >  static BLOCKING_NOTIFIER_HEAD(mt_adistance_algorithms);
>> >
>> > +static DEFINE_MUTEX(default_dram_perf_lock);
>>
>> Better to add comments about what is protected by this lock.
>>
>
> Thank you. I will add a comment like this:
> + /* The lock is used to protect `default_dram_perf*` info and nid. */
> +static DEFINE_MUTEX(default_dram_perf_lock);
>
> I also found an error path was not handled and
> found the lock could be put closer to what it protects.
> I will have them fixed in V5.
>
>> >  static bool default_dram_perf_error;
>> >  static struct access_coordinate default_dram_perf;
>> >  static int default_dram_perf_ref_nid = NUMA_NO_NODE;
>> > @@ -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 *mtype;
>>
>> mtype may be referenced without initialization now below.
>>
>
> Good catch! Thank you.
>
> Please check below.
> I may found a potential NULL pointer dereference.
>
>> > +     int adist = MEMTIER_ADISTANCE_DRAM;
>> >       pg_data_t *pgdat = NODE_DATA(node);
>> >
>> >
>> > @@ -514,11 +521,20 @@ 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 (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");
>> > +             }
>> > +     }
>> >
>> > -     memtype = node_memory_types[node].memtype;
>> > -     node_set(node, memtype->nodes);
>> > -     memtier = find_create_memory_tier(memtype);
>> > +     __init_node_memory_type(node, mtype);
>> > +
>> > +     mtype = node_memory_types[node].memtype;
>> > +     node_set(node, mtype->nodes);
>
> If the `mtype` could be NULL, would there be a potential
> NULL pointer dereference. Do you have a preferred idea
> to fix this if needed?

Initialize mtype with default_dram_type?

>> > +     memtier = find_create_memory_tier(mtype);
>> >       if (!IS_ERR(memtier))
>> >               rcu_assign_pointer(pgdat->memtier, memtier);
>> >       return memtier;
>> > @@ -655,6 +671,34 @@ void mt_put_memory_types(struct list_head *memory_types)
>> >  }
>> >  EXPORT_SYMBOL_GPL(mt_put_memory_types);
>> >

[snip]

--
Best Regards,
Huang, Ying

On Mon, Mar 25, 2024 at 8:08 PM Huang, Ying <ying.huang@intel.com> wrote:
>
> "Ho-Ren (Jack) Chuang" <horenchuang@bytedance.com> writes:
>
> > On Fri, Mar 22, 2024 at 1:41 AM Huang, Ying <ying.huang@intel.com> wrote:
> >>
> >> "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.
> >> >
> >> > * 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.
> >> >
> >> > * 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.
> >> >
> >> > * Introduce another new lock `default_dram_perf_lock` for adist calculation
> >> > 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 `default_dram_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>
> >> > ---
> >> >  mm/memory-tiers.c | 73 ++++++++++++++++++++++++++++++++++++++++-------
> >> >  1 file changed, 63 insertions(+), 10 deletions(-)
> >> >
> >> > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> >> > index 974af10cfdd8..9396330fa162 100644
> >> > --- a/mm/memory-tiers.c
> >> > +++ b/mm/memory-tiers.c
> >> > @@ -36,6 +36,11 @@ 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;
> >> >
> >> > @@ -108,6 +113,7 @@ static struct demotion_nodes *node_demotion __read_mostly;
> >> >
> >> >  static BLOCKING_NOTIFIER_HEAD(mt_adistance_algorithms);
> >> >
> >> > +static DEFINE_MUTEX(default_dram_perf_lock);
> >>
> >> Better to add comments about what is protected by this lock.
> >>
> >
> > Thank you. I will add a comment like this:
> > + /* The lock is used to protect `default_dram_perf*` info and nid. */
> > +static DEFINE_MUTEX(default_dram_perf_lock);
> >
> > I also found an error path was not handled and
> > found the lock could be put closer to what it protects.
> > I will have them fixed in V5.
> >
> >> >  static bool default_dram_perf_error;
> >> >  static struct access_coordinate default_dram_perf;
> >> >  static int default_dram_perf_ref_nid = NUMA_NO_NODE;
> >> > @@ -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 *mtype;
> >>
> >> mtype may be referenced without initialization now below.
> >>
> >
> > Good catch! Thank you.
> >
> > Please check below.
> > I may found a potential NULL pointer dereference.
> >
> >> > +     int adist = MEMTIER_ADISTANCE_DRAM;
> >> >       pg_data_t *pgdat = NODE_DATA(node);
> >> >
> >> >
> >> > @@ -514,11 +521,20 @@ 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 (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");
> >> > +             }
> >> > +     }
> >> >
> >> > -     memtype = node_memory_types[node].memtype;
> >> > -     node_set(node, memtype->nodes);
> >> > -     memtier = find_create_memory_tier(memtype);
> >> > +     __init_node_memory_type(node, mtype);
> >> > +
> >> > +     mtype = node_memory_types[node].memtype;
> >> > +     node_set(node, mtype->nodes);
> >
> > If the `mtype` could be NULL, would there be a potential
> > NULL pointer dereference. Do you have a preferred idea
> > to fix this if needed?
>
> Initialize mtype with default_dram_type?
>

Sounds like a plan. Thank you. I'm working on V5.

>
> >> > +     memtier = find_create_memory_tier(mtype);
> >> >       if (!IS_ERR(memtier))
> >> >               rcu_assign_pointer(pgdat->memtier, memtier);
> >> >       return memtier;
> >> > @@ -655,6 +671,34 @@ void mt_put_memory_types(struct list_head *memory_types)
> >> >  }
> >> >  EXPORT_SYMBOL_GPL(mt_put_memory_types);
> >> >
>
> [snip]
>
> --
> Best Regards,
> Huang, Ying