Message-ID: <87k07slnt7.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Mon, 01 Aug 2022 10:06:44 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Wei Xu <weixugc@...gle.com>, Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.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>,
        Johannes Weiner <hannes@...xchg.org>, jvgediya.oss@...il.com
Subject: Re: [PATCH v11 4/8] mm/demotion/dax/kmem: Set node's abstract
 distance to MEMTIER_ADISTANCE_PMEM

"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:

> "Huang, Ying" <ying.huang@...el.com> writes:
>
>> "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> 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@...ux.ibm.com>
>>> ---
>>>  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().

Best Regards,
Huang, Ying

> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 6b0d5de9a3e9..eb4e158012a9 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -248,6 +248,7 @@ static void __exit dax_kmem_exit(void)
>  	dax_driver_unregister(&device_dax_kmem_driver);
>  	if (!any_hotremove_failed)
>  		kfree_const(kmem_name);
> +	unregister_memory_type(&default_pmem_type);
>  }
>  
>  MODULE_AUTHOR("Intel Corporation");
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index fc6b7a14da51..8355baf5b8b4 100644
> --- a/include/linux/memory-tiers.h
> +++ b/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 unregister_memory_type(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)
> +{
>  
>  }
>  
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 064e0f932795..4d29ebd4c4f3 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -500,6 +500,28 @@ void init_node_memory_type(int node, struct memory_dev_type *default_type)
>  	mutex_unlock(&memory_tier_lock);
>  }
>  
> +void unregister_memory_type(struct memory_dev_type *memtype)
> +{
> +	int node;
> +	struct memory_tier *memtier = memtype->memtier;
> +
> +	mutex_lock(&memory_tier_lock);
> +	for(node = 0; node < MAX_NUMNODES; node++) {
> +		if (node_memory_types[node] == memtype) {
> +			if (!nodes_empty(memtype->nodes))
> +				WARN_ON(1);
> +			node_memory_types[node] = NULL;
> +		}
> +	}
> +
> +	list_del(&memtype->tier_sibiling);
> +	memtype->memtier = NULL;
> +	if (list_empty(&memtier->memory_types))
> +		destroy_memory_tier(memtier);
> +
> +	mutex_unlock(&memory_tier_lock);
> +}
> +
>  void update_node_adistance(int node, struct memory_dev_type *memtype)
>  {
>  	pg_data_t *pgdat;

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