Re: [PATCH v2 1/1] memory tier: consolidate the initialization of memory tiers

[Huang, Ying]

Jonathan Cameron <Jonathan.Cameron@Huawei.com> writes:

> On Fri, 28 Jun 2024 06:09:23 +0000
> "Ho-Ren (Jack) Chuang" <horen.chuang@linux.dev> wrote:

[snip]

>> @@ -875,8 +886,7 @@ static int __meminit memtier_hotplug_callback(struct 
>> notifier_block *self,
>>  
>>  static int __init memory_tier_init(void)
>>  {
>> -    int ret, node;
>> -    struct memory_tier *memtier;
>> +    int ret;
>>  
>>      ret = subsys_virtual_register(&memory_tier_subsys, NULL);
>>      if (ret)
>> @@ -887,7 +897,8 @@ static int __init memory_tier_init(void)
>>                              GFP_KERNEL);
>>      WARN_ON(!node_demotion);
>>  #endif
>> -    mutex_lock(&memory_tier_lock);
>> +
>> +    guard(mutex)(&memory_tier_lock);
>
> If this was safe to do without the rest of the change (I think so)
> then better to pull that out as a trivial precursor so less noise
> in here.
>
>>      /*
>>       * For now we can have 4 faster memory tiers with smaller adistance
>>       * than default DRAM tier.
>> @@ -897,29 +908,9 @@ static int __init memory_tier_init(void)
>>      if (IS_ERR(default_dram_type))
>>              panic("%s() failed to allocate default DRAM tier\n", __func__);
>>  
>> -    /*
>> -     * Look at all the existing N_MEMORY nodes and add them to
>> -     * default memory tier or to a tier if we already have memory
>> -     * 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))
>> -                    /*
>> -                     * Continue with memtiers we are able to setup
>> -                     */
>> -                    break;
>> -    }
>> -    establish_demotion_targets();
>> -    mutex_unlock(&memory_tier_lock);
>> +    /* Record nodes with memory and CPU to set default DRAM performance. */
>> +    nodes_and(default_dram_nodes, node_states[N_MEMORY],
>> +              node_states[N_CPU]);
>
> There are systems where (for various esoteric reasons, such as describing an
> association with some other memory that isn't DRAM where the granularity
> doesn't match) the CPU nodes contain no DRAM but rather it's one node away.
> Handling that can be a job for another day though.
>
> Why does this need to be computed here?  Why not do it in
> hmat_set_default_dram_perf? Doesn't seem to be used anywhere else.

IMO, which node is default dram node is a general concept instead of
HMAT specific.  So, I think that it's better to decide that in the
general code (memory-tiers.c).

>>  
>>      hotplug_memory_notifier(memtier_hotplug_callback, MEMTIER_HOTPLUG_PRI);
>>      return 0;

--
Best Regards,
Huang, Ying