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

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Date:   Mon, 6 Jun 2022 18:30:51 +0530
From:   Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To:     Bharata B Rao <bharata@....com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org
Cc:     Huang Ying <ying.huang@...el.com>,
        Greg Thelen <gthelen@...gle.com>,
        Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.com>,
        Brice Goglin <brice.goglin@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Feng Tang <feng.tang@...el.com>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [RFC PATCH v4 4/7] mm/demotion/dax/kmem: Set node's memory tier
 to MEMORY_TIER_PMEM

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@...ux.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;