Re: [External] Re: [PATCH v3 1/2] memory tier: dax/kmem: create CPUless memory tiers after obtaining HMAT info

[Ho-Ren (Jack) Chuang]

On Wed, Mar 20, 2024 at 12:15 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.
> >
> > 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.
>

I will make mt_find_alloc/mt_put_memory_type changes as
a separate patch and the first of my patch series. Thanks.


> > 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.
>

Thanks. I will remove it.

> >  #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?
>

Yes, I will consolidate them.


> > +     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");
>                 }
>         }
>

Sounds good! I will do.


> > +     __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.
>

Got it. Thanks.
"
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(
> > @@ -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.
>

I will move it closer to default_dram_perf*.
And change it to:
+/*
+ * The lock is used to protect 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



-- 
Best regards,
Ho-Ren (Jack) Chuang
莊賀任