Re: [PATCH v11 4/8] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_ADISTANCE_PMEM

[Aneesh Kumar K V]

On 8/1/22 10:40 AM, Huang, Ying wrote:
> Aneesh Kumar K V <aneesh.kumar@xxxxxxxxxxxxx> writes:
> 
>> On 8/1/22 7:36 AM, Huang, Ying wrote:
>>> "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> writes:
>>>
>>>> "Huang, Ying" <ying.huang@xxxxxxxxx> writes:
>>>>
>>>>> "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> writes:
>>>>>
>>>>>> By default, all nodes are assigned to the default memory tier which
>>>>>> is the memory tier designated for nodes with DRAM
>>>>>>
>>>>>> Set dax kmem device node's tier to slower memory tier by assigning
>>>>>> abstract distance to MEMTIER_ADISTANCE_PMEM. PMEM tier
>>>>>> appears below the default memory tier in demotion order.
>>>>>>
>>>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
>>>>>> ---
>>>>>>  drivers/dax/kmem.c           |  9 +++++++++
>>>>>>  include/linux/memory-tiers.h | 19 ++++++++++++++++++-
>>>>>>  mm/memory-tiers.c            | 28 ++++++++++++++++------------
>>>>>>  3 files changed, 43 insertions(+), 13 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
>>>>>> index a37622060fff..6b0d5de9a3e9 100644
>>>>>> --- a/drivers/dax/kmem.c
>>>>>> +++ b/drivers/dax/kmem.c
>>>>>> @@ -11,6 +11,7 @@
>>>>>>  #include <linux/fs.h>
>>>>>>  #include <linux/mm.h>
>>>>>>  #include <linux/mman.h>
>>>>>> +#include <linux/memory-tiers.h>
>>>>>>  #include "dax-private.h"
>>>>>>  #include "bus.h"
>>>>>>  
>>>>>> @@ -41,6 +42,12 @@ struct dax_kmem_data {
>>>>>>  	struct resource *res[];
>>>>>>  };
>>>>>>  
>>>>>> +static struct memory_dev_type default_pmem_type  = {
>>>>>
>>>>> Why is this named as default_pmem_type?  We will not change the memory
>>>>> type of a node usually.
>>>>>
>>>>
>>>> Any other suggestion? pmem_dev_type? 
>>>
>>> Or dax_pmem_type?
>>>
>>> DAX is used to enumerate the memory device.
>>>
>>>>
>>>>>> +	.adistance = MEMTIER_ADISTANCE_PMEM,
>>>>>> +	.tier_sibiling = LIST_HEAD_INIT(default_pmem_type.tier_sibiling),
>>>>>> +	.nodes  = NODE_MASK_NONE,
>>>>>> +};
>>>>>> +
>>>>>>  static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>>>>>>  {
>>>>>>  	struct device *dev = &dev_dax->dev;
>>>>>> @@ -62,6 +69,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>>>>>>  		return -EINVAL;
>>>>>>  	}
>>>>>>  
>>>>>> +	init_node_memory_type(numa_node, &default_pmem_type);
>>>>>> +
>>>>>
>>>>> The memory hot-add below may fail.  So the error handling needs to be
>>>>> added.
>>>>>
>>>>> And, it appears that the memory type and memory tier of a node may be
>>>>> fully initialized here before NUMA hot-adding started.  So I suggest to
>>>>> set node_memory_types[] here only.  And set memory_dev_type->nodes in
>>>>> node hot-add callback.  I think there is the proper place to complete
>>>>> the initialization.
>>>>>
>>>>> And, in theory dax/kmem.c can be unloaded.  So we need to clear
>>>>> node_memory_types[] for nodes somewhere.
>>>>>
>>>>
>>>> I guess by module exit we can be sure that all the memory managed
>>>> by dax/kmem is hotplugged out. How about something like below?
>>>
>>> Because we set node_memorty_types[] in dev_dax_kmem_probe(), it's
>>> natural to clear it in dev_dax_kmem_remove().
>>>
>>
>> Most of required reset/clear is done as part of memory hotunplug. So
>> if we did manage to successfully unplug the memory, everything except
>> node_memory_types[node] should be reset. That makes the clear_node_memory_type
>> the below. 
>>
>> void clear_node_memory_type(int node, struct memory_dev_type *memtype)
>> {
>>
>> 	mutex_lock(&memory_tier_lock);
>> 	/*
>> 	 * memory unplug did clear the node from the memtype and
>> 	 * dax/kem did initialize this node's memory type.
>> 	 */
>> 	if (!node_isset(node, memtype->nodes) && node_memory_types[node]  == memtype){
>> 		node_memory_types[node] = NULL;
>> 	}
>> 	mutex_unlock(&memory_tier_lock);
>> }
>>
>> With the module unload, it is kind of force removing the usage of the specific memtype.
>> Considering module unload will remove the usage of specific memtype from other parts
>> of the kernel and we already do all the required reset in memory hot unplug, do we
>> need to do the clear_node_memory_type above? 
> 
> Per my understanding, we need to call clear_node_memory_type() in
> dev_dax_kmem_remove().  After that, we have nothing to do in
> dax_kmem_exit().
> 

Ok, I guess you are suggesting to do the clear_node_memory_type even if we fail the memory remove. 
Should we also rebuild demotion order? On a successful memory remove we do rebuild demotion order.
This is what i ended up with.

modified   drivers/dax/kmem.c
@@ -171,6 +171,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
 {
 	int i, success = 0;
+	int node = dev_dax->target_node;
 	struct device *dev = &dev_dax->dev;
 	struct dax_kmem_data *data = dev_get_drvdata(dev);
 
@@ -208,6 +209,12 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
 		kfree(data);
 		dev_set_drvdata(dev, NULL);
 	}
+	/*
+	 * Clear the memtype association, even if the memory
+	 * remove failed.
+	 */
+	clear_node_memory_type(node, dax_pmem_type);
+
 }
 #else
 static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
modified   include/linux/memory-tiers.h
@@ -31,6 +31,7 @@ struct memory_dev_type {
 #ifdef CONFIG_NUMA
 extern bool numa_demotion_enabled;
 void init_node_memory_type(int node, struct memory_dev_type *default_type);
+void clear_node_memory_type(int node, struct memory_dev_type *memtype);
 #ifdef CONFIG_MIGRATION
 int next_demotion_node(int node);
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
@@ -57,6 +58,10 @@ static inline bool node_is_toptier(int node)
 #define numa_demotion_enabled	false
 static inline void init_node_memory_type(int node, struct memory_dev_type *default_type)
 {
+}
+
+static inline void unregister_memory_type(struct memory_dev_type *memtype)
+{
 
 }
 
modified   mm/memory-tiers.c
@@ -501,6 +501,36 @@ void init_node_memory_type(int node, struct memory_dev_type *default_type)
 }
 EXPORT_SYMBOL_GPL(init_node_memory_type);
 
+void clear_node_memory_type(int node, struct memory_dev_type *memtype)
+{
+	struct memory_tier *memtier;
+
+	mutex_lock(&memory_tier_lock);
+	/*
+	 * Even if we fail to unplug memory, clear the association of
+	 * this node to this specific memory type.
+	 */
+	if (node_memory_types[node] == memtype) {
+
+		memtier = __node_get_memory_tier(node);
+		if (memtier) {
+			rcu_assign_pointer(pgdat->memtier, NULL);
+			synchronize_rcu();
+		}
+		node_clear(node, memtype->nodes);
+		if (nodes_empty(memtype->nodes)) {
+			list_del(&memtype->tier_sibiling);
+			memtype->memtier = NULL;
+			if (current_memtier && list_empty(&current_memtier->memory_types))
+				destroy_memory_tier(current_memtier);
+
+		}
+		node_memory_types[node] = NULL;
+	}
+	mutex_unlock(&memory_tier_lock);
+}
+EXPORT_SYMBOL_GPL(init_node_memory_type);
+
 void update_node_adistance(int node, struct memory_dev_type *memtype)
 {
 	pg_data_t *pgdat;

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