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

["Huang, Ying" <ying.huang@intel.com>]

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