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

Ho-Ren (Jack) Chuang
2024-04-04T00:21:33Z

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@huawei.com> 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