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

["Huang, Ying" <ying.huang@intel.com>]

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

> On 8/1/22 7:36 AM, Huang, Ying wrote:
>> "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
>> 
>>> "Huang, Ying" <ying.huang@intel.com> writes:
>>>
>>>> "Aneesh Kumar K.V" <aneesh.kumar@linux.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@linux.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().
>> 
>
> 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().

Best Regards,
Huang, Ying