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From: "Huang, Ying" <ying.huang@intel.com>
To: "Ho-Ren (Jack) Chuang" <horenchuang@bytedance.com>
Cc: Gregory Price <gourry.memverge@gmail.com>,  aneesh.kumar@linux.ibm.com,
  mhocko@suse.com,  tj@kernel.org,  john@jagalactic.com,  Eishan Mirakhur
 <emirakhur@micron.com>,  Vinicius Tavares Petrucci
 <vtavarespetr@micron.com>,  Ravis OpenSrc <Ravis.OpenSrc@micron.com>,
  Alistair Popple <apopple@nvidia.com>,  "Rafael J. Wysocki"
 <rafael@kernel.org>,  Len Brown <lenb@kernel.org>,  Dan Williams
 <dan.j.williams@intel.com>,  Vishal Verma <vishal.l.verma@intel.com>,
  Dave Jiang <dave.jiang@intel.com>,  Andrew Morton
 <akpm@linux-foundation.org>,  Jonathan Cameron
 <Jonathan.Cameron@huawei.com>,  linux-acpi@vger.kernel.org,
  linux-kernel@vger.kernel.org,  nvdimm@lists.linux.dev,
  linux-cxl@vger.kernel.org,  linux-mm@kvack.org,  "Ho-Ren (Jack) Chuang"
 <horenc@vt.edu>,  "Ho-Ren (Jack) Chuang" <horenchuang@gmail.com>,
  qemu-devel@nongnu.org,  Hao Xiang <hao.xiang@bytedance.com>
Subject: Re: [External] Re: [PATCH v2 1/1] memory tier: acpi/hmat: create
 CPUless memory tiers after obtaining HMAT info
In-Reply-To: <CAKPbEqpTNN5GKKCXmyTv0szpL-N1pdKFZYPHCJjyhgpKZGMiWw@mail.gmail.com>
	(Ho-Ren Chuang's message of "Wed, 13 Mar 2024 01:16:27 -0700")
References: <20240312061729.1997111-1-horenchuang@bytedance.com>
	<20240312061729.1997111-2-horenchuang@bytedance.com>
	<874jdb4xk8.fsf@yhuang6-desk2.ccr.corp.intel.com>
	<CAKPbEqpTNN5GKKCXmyTv0szpL-N1pdKFZYPHCJjyhgpKZGMiWw@mail.gmail.com>
Date: Thu, 14 Mar 2024 15:52:07 +0800
Message-ID: <8734st2qu0.fsf@yhuang6-desk2.ccr.corp.intel.com>
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"Ho-Ren (Jack) Chuang" <horenchuang@bytedance.com> writes:

> On Tue, Mar 12, 2024 at 2:21=E2=80=AFAM 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 m=
emory
>> > (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 pro=
cess
>> > 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.
>>
>
> Will do! Thanks,
>
>
>>
>> > 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 informa=
tion.
>> > 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 en=
d up
>> > trying to acquire the same lock, leading to a potential deadlock.
>> > Therefore, we propose introducing a standalone `mt_perf_lock` to prote=
ct
>> > `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.
>
> I can put it back in memory-tier.c. How about the list? Do we still
> need to keep a separate list for storing late_inited memory nodes?
> And how about the list name if we need to remove the prefix "hmat_"?

I don't think we need a separate list for memory-less nodes.  Just
iterate all memory-less nodes.

>
>> Instead, if the memory_type of a
>> node isn't set by the driver, we should manage it in memory-tier.c as
>> fallback.
>>
>
> Do you mean some device drivers may init memory tiers between
> memory_tier_init() and late_initcall(memory_tier_late_init);?
> And this is the reason why you mention to exclude
> "node_memory_types[nid].memtype !=3D NULL" in memory_tier_late_init().
> Is my understanding correct?

Yes.

>> >  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.
>>
>
> Thanks. Learned!
>
>
>> >       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 =3D false;
>> >       struct memory_dev_type *mtype;
>> >
>> >       mutex_lock(&kmem_memory_type_lock);
>> > -     list_for_each_entry(mtype, &kmem_memory_types, list) {
>> > -             if (mtype->adistance =3D=3D adist) {
>> > -                     found =3D true;
>> > -                     break;
>> > -             }
>> > -     }
>> > -     if (!found) {
>> > -             mtype =3D alloc_memory_type(adist);
>> > -             if (!IS_ERR(mtype))
>> > -                     list_add(&mtype->list, &kmem_memory_types);
>> > -     }
>> > +     mtype =3D 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 *c=
oord);
>> > +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 acc=
ess_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.
>>
>
> Where is better for me to add comments for this? Code? Patch description?
> Will put it closer to the protected data. Thanks.

Just put the comments at the above of the lock in the source code.

>
>
>> >  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 memo=
ry_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 =3D false;
>> > +     struct memory_dev_type *mtype;
>> > +
>> > +     list_for_each_entry(mtype, memory_types, list) {
>> > +             if (mtype->adistance =3D=3D adist) {
>> > +                     found =3D true;
>> > +                     break;
>> > +             }
>> > +     }
>> > +     if (!found) {
>> > +             mtype =3D 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 =3D NULL;
>> > +     int adist =3D MEMTIER_ADISTANCE_DRAM;
>> > +
>> > +     mt_calc_adistance(node, &adist);
>> > +     if (adist !=3D MEMTIER_ADISTANCE_DRAM) {
>>
>> We can manage default_dram_type() via find_alloc_memory_type()
>> too.
>>
>> And, if "node_memory_types[node].memtype =3D=3D 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 =3D 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 !=3D NULL".  Some memo=
ry
>> 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 ch=
ar *prefix)
>> >  {
>> >       pr_info(
>> > @@ -636,7 +690,7 @@ int mt_set_default_dram_perf(int nid, struct acces=
s_coordinate *perf,
>> >  {
>> >       int rc =3D 0;
>> >
>> > -     mutex_lock(&memory_tier_lock);
>> > +     mutex_lock(&mt_perf_lock);
>> >       if (default_dram_perf_error) {
>> >               rc =3D -EIO;
>> >               goto out;
>> > @@ -684,7 +738,7 @@ int mt_set_default_dram_perf(int nid, struct acces=
s_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 =3D=3D 0)
>> >               return -EINVAL;
>> >
>> > -     mutex_lock(&memory_tier_lock);
>> > +     mutex_lock(&mt_perf_lock);
>> >       /*
>> >        * The abstract distance of a memory node is in direct proportio=
n 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.writ=
e_latency) *
>> >               (default_dram_perf.read_bandwidth + default_dram_perf.wr=
ite_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 n=
uma nodes.
>> > +                      * These will be initialized when HMAT informati=
on is
>>
>> HMAT is platform specific, we should avoid to mention it in general code
>> if possible.
>>
>
> Will fix! Thanks,
>
>
>> > +                      * available.
>> > +                      */
>> > +                     continue;
>> > +
>> >               memtier =3D set_node_memory_tier(node);
>> >               if (IS_ERR(memtier))
>> >                       /*
>>

--
Best Regards,
Huang, Ying