Re: [PATCH v10 2/2] memory tier: create CPUless memory tiers after obtaining HMAT info

[Ho-Ren (Jack) Chuang]

Hi Jonathan,

Thank you for your feedback. I will fix them (inlined) in the next V11.

On Wed, Apr 3, 2024 at 10:04 AM Jonathan Cameron
<Jonathan.Cameron@xxxxxxxxxx> wrote:
>
> A few minor comments inline.
>
> > diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> > index a44c03c2ba3a..16769552a338 100644
> > --- a/include/linux/memory-tiers.h
> > +++ b/include/linux/memory-tiers.h
> > @@ -140,12 +140,13 @@ 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)
> > +static inline struct memory_dev_type *mt_find_alloc_memory_type(int adist,
> > +                                     struct list_head *memory_types)
> >  {
> >       return NULL;
> >  }
> >
> > -void mt_put_memory_types(struct list_head *memory_types)
> > +static inline void mt_put_memory_types(struct list_head *memory_types)
> >  {
> Why in this patch and not previous one?

I've also noticed this issue. I will fix it in the next V11.

> >
> >  }
> > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> > index 974af10cfdd8..44fa10980d37 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 +113,8 @@ static struct demotion_nodes *node_demotion __read_mostly;
> >
> >  static BLOCKING_NOTIFIER_HEAD(mt_adistance_algorithms);
> >
> > +/* The lock is used to protect `default_dram_perf*` info and nid. */
> > +static DEFINE_MUTEX(default_dram_perf_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 +512,8 @@ 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 = default_dram_type;
>
> Does the rename add anything major to the patch?
> If not I'd leave it alone to reduce the churn and give
> a more readable patch.  If it is worth doing perhaps
> a precursor patch?
>

Either name works. Keeping it the same name will make the code
easier to follow. I agree! Thanks.

> > +     int adist = MEMTIER_ADISTANCE_DRAM;
> >       pg_data_t *pgdat = NODE_DATA(node);
> >
> >
> > @@ -514,11 +522,20 @@ 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");
> > +             }
> > +     }
> > +
> > +     __init_node_memory_type(node, mtype);
> >
> > -     memtype = node_memory_types[node].memtype;
> > -     node_set(node, memtype->nodes);
> > -     memtier = find_create_memory_tier(memtype);
> > +     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 +672,33 @@ 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_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.
> > +                      */
>
> Does the comment refer to this path, or to ones where memtype is set?
>

Yes, the comment is for explaining why the if condition is used.

> > +                     set_node_memory_tier(nid);
>
> Given the large comment I would add {} to help with readability.
> You could flip the logic to reduce indent
>         for_each_node_state(nid, N_MEMORY) {
>                 if (node_memory_types[nid].memtype)
>                         continue;
>                 /*
>                  * 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);
>
>

I will change it accordingly.

> > +
> > +     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);
>
> As below, this is a classic case where guard() will help readability.
>

I will change it accordingly.

> >       if (default_dram_perf_error) {
> >               rc = -EIO;
> >               goto out;
> > @@ -716,23 +760,30 @@ 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;
> >  }
> >
> >  int mt_perf_to_adistance(struct access_coordinate *perf, int *adist)
> >  {
> > -     if (default_dram_perf_error)
> > -             return -EIO;
> > +     int rc = 0;
>
> Looks like rc is set in all paths that reach where it issued.
>

Using guard(mutex), I will no longer need `int rc`.
Replace `rc =` with `return XXX`.

> >
> > -     if (default_dram_perf_ref_nid == NUMA_NO_NODE)
> > -             return -ENOENT;
> > +     mutex_lock(&default_dram_perf_lock);
>
> This would benefit quite a lot from
> guard(mutex)(&default_dram_perf_lock);
> and direct returns throughout.
>

Got it. I will change it accordingly.

>
> > +     if (default_dram_perf_error) {
> > +             rc = -EIO;
> > +             goto out;
> > +     }
> >
> >       if (perf->read_latency + perf->write_latency == 0 ||
> > -         perf->read_bandwidth + perf->write_bandwidth == 0)
> > -             return -EINVAL;
> > +         perf->read_bandwidth + perf->write_bandwidth == 0) {
> > +             rc = -EINVAL;
> > +             goto out;
> > +     }
> >
> > -     mutex_lock(&memory_tier_lock);
> > +     if (default_dram_perf_ref_nid == NUMA_NO_NODE) {
> > +             rc = -ENOENT;
> > +             goto out;
> > +     }
> >       /*
> >        * The abstract distance of a memory node is in direct proportion to
> >        * its memory latency (read + write) and inversely proportional to its
> > @@ -745,9 +796,10 @@ 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);
> >
> > -     return 0;
> > +out:
> > +     mutex_unlock(&default_dram_perf_lock);
> > +     return rc;
> >  }
> >  EXPORT_SYMBOL_GPL(mt_perf_to_adistance);
> >
> > @@ -858,7 +910,8 @@ 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);
>
> Unusual indenting.  Align with just after (
>

Aligning with "(" will exceed 100 columns. Would that be acceptable?

> >       if (IS_ERR(default_dram_type))
> >               panic("%s() failed to allocate default DRAM tier\n", __func__);
> >
> > @@ -868,6 +921,14 @@ 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
>
> I think this wraps at just over 80 chars.  Seems silly to wrap so tightly and not
> quite fit under 80. (this is about 83 chars.
>

I can fix this.
I have a question. From my patch, this is <80 chars. However,
in an email, this is >80 chars. Does that mean we need to
count the number of chars in an email, not in a patch? Or if I
missed something? like vim configuration or?

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


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