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

[Aneesh Kumar K V]

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@xxxxxxxxxxxxx> 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;