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

Aneesh Kumar K V
2022-06-06T13:01:33Z

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;