Re: [PATCH v10 3/8] mm/demotion: Add hotplug callbacks to handle new numa node onlined

[Huang, Ying]

Aneesh Kumar K V <aneesh.kumar@xxxxxxxxxxxxx> writes:

> On 7/26/22 9:33 AM, Huang, Ying wrote:
>> "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> writes:
>> 
>>> If the new NUMA node onlined doesn't have a performance level assigned,
>>> the kernel adds the NUMA node to default memory tier.
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
>>> ---
>>>  include/linux/memory-tiers.h |  1 +
>>>  mm/memory-tiers.c            | 75 ++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 76 insertions(+)
>>>
>>> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
>>> index ef380a39db3a..3d5f14d57ae6 100644
>>> --- a/include/linux/memory-tiers.h
>>> +++ b/include/linux/memory-tiers.h
>>> @@ -14,6 +14,7 @@
>>>  #define MEMTIER_PERF_LEVEL_DRAM	(1 << (MEMTIER_CHUNK_BITS + 2))
>>>  /* leave one tier below this slow pmem */
>>>  #define MEMTIER_PERF_LEVEL_PMEM	(1 << MEMTIER_CHUNK_BITS)
>>> +#define MEMTIER_HOTPLUG_PRIO	100
>>>  
>>>  extern bool numa_demotion_enabled;
>>>  
>>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>>> index 41a21cc5ae55..cc3a47ec18e4 100644
>>> --- a/mm/memory-tiers.c
>>> +++ b/mm/memory-tiers.c
>>> @@ -5,6 +5,7 @@
>>>  #include <linux/lockdep.h>
>>>  #include <linux/moduleparam.h>
>>>  #include <linux/node.h>
>>> +#include <linux/memory.h>
>>>  #include <linux/memory-tiers.h>
>>>  
>>>  struct memory_tier {
>>> @@ -64,6 +65,78 @@ static struct memory_tier *find_create_memory_tier(unsigned int perf_level)
>>>  	return new_memtier;
>>>  }
>>>  
>>> +static struct memory_tier *__node_get_memory_tier(int node)
>>> +{
>>> +	struct memory_tier *memtier;
>>> +
>>> +	list_for_each_entry(memtier, &memory_tiers, list) {
>>> +		if (node_isset(node, memtier->nodelist))
>>> +			return memtier;
>>> +	}
>>> +	return NULL;
>>> +}
>>> +
>>> +static void init_node_memory_tier(int node)
>> 
>> set_node_memory_tier()?
>
> That was done based on feedback from Alistair 
>
> https://lore.kernel.org/linux-mm/87h73iapg1.fsf@nvdebian.thelocal
>
>> 
>>> +{
>>> +	int perf_level;
>>> +	struct memory_tier *memtier;
>>> +
>>> +	mutex_lock(&memory_tier_lock);
>>> +
>>> +	memtier = __node_get_memory_tier(node);
>>> +	if (!memtier) {
>>> +		perf_level = node_devices[node]->perf_level;
>>> +		memtier = find_create_memory_tier(perf_level);
>>> +		node_set(node, memtier->nodelist);
>>> +	}

It's related to Alistair's comments too.  When will memtier != NULL
here?  We may need just VM_WARN_ON() here?

>>> +	mutex_unlock(&memory_tier_lock);
>>> +}
>>> +
>>> +static void clear_node_memory_tier(int node)
>>> +{
>>> +	struct memory_tier *memtier;
>>> +
>>> +	mutex_lock(&memory_tier_lock);
>>> +	memtier = __node_get_memory_tier(node);
>>> +	if (memtier)
>>> +		node_clear(node, memtier->nodelist);
>> 
>> When memtier->nodelist becomes empty, we need to free memtier?
>> 
>>> +	mutex_unlock(&memory_tier_lock);
>>> +}
>>> +
>>> +/*
>>> + * This runs whether reclaim-based migration is enabled or not,
>>> + * which ensures that the user can turn reclaim-based migration
>>> + * at any time without needing to recalculate migration targets.
>>> + */
>> 
>> The comments doesn't apply here.
>> 
>>> +static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
>>> +						 unsigned long action, void *_arg)
>> 
>> Now we are building memory tiers instead of working on demotion.  So I
>> think we should rename the function to memtier_hotplug_callback().
>> 
>>> +{
>>> +	struct memory_notify *arg = _arg;
>>> +
>>> +	/*
>>> +	 * Only update the node migration order when a node is
>>> +	 * changing status, like online->offline.
>>> +	 */
>>> +	if (arg->status_change_nid < 0)
>>> +		return notifier_from_errno(0);
>>> +
>>> +	switch (action) {
>>> +	case MEM_OFFLINE:
>>> +		clear_node_memory_tier(arg->status_change_nid);
>>> +		break;
>>> +	case MEM_ONLINE:
>>> +		init_node_memory_tier(arg->status_change_nid);
>>> +		break;
>>> +	}
>>> +
>>> +	return notifier_from_errno(0);
>>> +}
>>> +
>>> +static void __init migrate_on_reclaim_init(void)
>>> +{
>>> +	hotplug_memory_notifier(migrate_on_reclaim_callback, MEMTIER_HOTPLUG_PRIO);
>>> +}
>> 
>> I suggest to call hotplug_memory_notifier() in memory_tier_init()
>> directly.  We are not working on demotion here.
>> 
>>> +
>>>  static int __init memory_tier_init(void)
>>>  {
>>>  	int node;
>>> @@ -96,6 +169,8 @@ static int __init memory_tier_init(void)
>>>  			node_property->perf_level = default_memtier_perf_level;
>>>  	}
>>>  	mutex_unlock(&memory_tier_lock);
>>> +
>>> +	migrate_on_reclaim_init();
>>>  	return 0;
>>>  }
>>>  subsys_initcall(memory_tier_init);
>> 
>> Best Regards,
>> Huang, Ying
>
>
> Will update the patch in next iteration to take care of other feedback.

Thanks!

Best Regards,
Huang, Ying