Re: [RFC PATCH v4 4/7] mm/demotion/dax/kmem: Set node's memory tier to MEMORY_TIER_PMEM

[Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>]

On 6/6/22 5:39 PM, Bharata B Rao wrote:
> On 6/6/2022 5:24 PM, Aneesh Kumar K.V wrote:
>> Aneesh Kumar K V <aneesh.kumar@linux.ibm.com> writes:
>>>
>> Can you try this change?
>>
>> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
>> index 7a11c387fbbc..905609260dda 100644
>> --- a/drivers/dax/kmem.c
>> +++ b/drivers/dax/kmem.c
>> @@ -94,6 +94,17 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>>   		goto err_reg_mgid;
>>   	data->mgid = rc;
>>   
>> +	/*
>> +	 * This get called before the node is brought online. That
>> +	 * is because depending on the value of mhp_default_online_type
>> +	 * the kernel will online the memory along with hotplug
>> +	 * operation. Add the new memory tier before we try to bring
>> +	 * memory blocks online. Otherwise new node will get added to
>> +	 * the default memory tier via hotplug callbacks.
>> +	 */
>> +#ifdef CONFIG_TIERED_MEMORY
>> +	node_set_memory_tier(numa_node, MEMORY_TIER_PMEM);
>> +#endif
>>   	for (i = 0; i < dev_dax->nr_range; i++) {
>>   		struct resource *res;
>>   		struct range range;
>> @@ -148,9 +159,6 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>>   
>>   	dev_set_drvdata(dev, data);
>>   
>> -#ifdef CONFIG_TIERED_MEMORY
>> -	node_set_memory_tier(numa_node, MEMORY_TIER_PMEM);
>> -#endif
>>   	return 0;
>>   
>>   err_request_mem:
> 
> Yes, this fixes the issue for me. Thanks.
> 

I might put the below change instead of the above. In the end I guess it 
is better to add a NUMA node to memory tier after the node is brought 
online than before even though with the current code it shouldn't matter 
much.

modified   drivers/dax/kmem.c
@@ -147,9 +147,15 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
  	}

  	dev_set_drvdata(dev, data);
-
+	/*
+	 * node_reset_memory_tier is used here to ensure we force
+	 * update the NUMA node memory tier. Depending on the value
+	 * of mhp_default_online_type the kernel will online the memory
+	 * blocks along with hotplug operation above. This can result in dax
+	 * kmem memory NUMA node getting added to default memory tier.
+	 */
  #ifdef CONFIG_TIERED_MEMORY
-	node_set_memory_tier(numa_node, MEMORY_TIER_PMEM);
+	node_reset_memory_tier(numa_node, MEMORY_TIER_PMEM);
  #endif
  	return 0;