Re: [External] Re: [PATCH v4 2/2] memory tier: create CPUless memory tiers after obtaining HMAT info

[Ho-Ren (Jack) Chuang]

On Fri, Mar 22, 2024 at 1:41 AM Huang, Ying <ying.huang@xxxxxxxxx> wrote:
>
> "Ho-Ren (Jack) Chuang" <horenchuang@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > Signed-off-by: Hao Xiang <hao.xiang@xxxxxxxxxxxxx>
> > ---
> >  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



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