Re: [PATCH v11 8/8] mm/demotion: Update node_is_toptier to work with memory tiers

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

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

> On 7/29/22 12:11 PM, Aneesh Kumar K V wrote:
>> On 7/29/22 12:09 PM, Huang, Ying wrote:
>>> "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
>>>
>>>> With memory tiers support we can have memory only NUMA nodes
>>>> in the top tier from which we want to avoid promotion tracking NUMA
>>>> faults. Update node_is_toptier to work with memory tiers.
>>>> All NUMA nodes are by default top tier nodes. With lower memory
>>>> tiers added we consider all memory tiers above a memory tier having
>>>> CPU NUMA nodes as a top memory tier
>>>>
>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>>> ---
>>>>  include/linux/memory-tiers.h | 11 ++++++++++
>>>>  include/linux/node.h         |  5 -----
>>>>  mm/huge_memory.c             |  1 +
>>>>  mm/memory-tiers.c            | 42 ++++++++++++++++++++++++++++++++++++
>>>>  mm/migrate.c                 |  1 +
>>>>  mm/mprotect.c                |  1 +
>>>>  6 files changed, 56 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
>>>> index f8dbeda617a7..bc9fb9d39b2c 100644
>>>> --- a/include/linux/memory-tiers.h
>>>> +++ b/include/linux/memory-tiers.h
>>>> @@ -35,6 +35,7 @@ struct memory_dev_type *init_node_memory_type(int node, struct memory_dev_type *
>>>>  #ifdef CONFIG_MIGRATION
>>>>  int next_demotion_node(int node);
>>>>  void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
>>>> +bool node_is_toptier(int node);
>>>>  #else
>>>>  static inline int next_demotion_node(int node)
>>>>  {
>>>> @@ -45,6 +46,11 @@ static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *target
>>>>  {
>>>>  	*targets = NODE_MASK_NONE;
>>>>  }
>>>> +
>>>> +static inline bool node_is_toptier(int node)
>>>> +{
>>>> +	return true;
>>>> +}
>>>>  #endif
>>>>  
>>>>  #else
>>>> @@ -64,5 +70,10 @@ static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *target
>>>>  {
>>>>  	*targets = NODE_MASK_NONE;
>>>>  }
>>>> +
>>>> +static inline bool node_is_toptier(int node)
>>>> +{
>>>> +	return true;
>>>> +}
>>>>  #endif	/* CONFIG_NUMA */
>>>>  #endif  /* _LINUX_MEMORY_TIERS_H */
>>>> diff --git a/include/linux/node.h b/include/linux/node.h
>>>> index 40d641a8bfb0..9ec680dd607f 100644
>>>> --- a/include/linux/node.h
>>>> +++ b/include/linux/node.h
>>>> @@ -185,9 +185,4 @@ static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
>>>>  
>>>>  #define to_node(device) container_of(device, struct node, dev)
>>>>  
>>>> -static inline bool node_is_toptier(int node)
>>>> -{
>>>> -	return node_state(node, N_CPU);
>>>> -}
>>>> -
>>>>  #endif /* _LINUX_NODE_H_ */
>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>>> index 834f288b3769..8405662646e9 100644
>>>> --- a/mm/huge_memory.c
>>>> +++ b/mm/huge_memory.c
>>>> @@ -35,6 +35,7 @@
>>>>  #include <linux/numa.h>
>>>>  #include <linux/page_owner.h>
>>>>  #include <linux/sched/sysctl.h>
>>>> +#include <linux/memory-tiers.h>
>>>>  
>>>>  #include <asm/tlb.h>
>>>>  #include <asm/pgalloc.h>
>>>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>>>> index 84e2be31a853..36d87dc422ab 100644
>>>> --- a/mm/memory-tiers.c
>>>> +++ b/mm/memory-tiers.c
>>>> @@ -30,6 +30,7 @@ static DEFINE_MUTEX(memory_tier_lock);
>>>>  static LIST_HEAD(memory_tiers);
>>>>  struct memory_dev_type *node_memory_types[MAX_NUMNODES];
>>>>  #ifdef CONFIG_MIGRATION
>>>> +static int top_tier_adistance;
>>>>  /*
>>>>   * node_demotion[] examples:
>>>>   *
>>>> @@ -159,6 +160,31 @@ static struct memory_tier *__node_get_memory_tier(int node)
>>>>  }
>>>>  
>>>>  #ifdef CONFIG_MIGRATION
>>>> +bool node_is_toptier(int node)
>>>> +{
>>>> +	bool toptier;
>>>> +	pg_data_t *pgdat;
>>>> +	struct memory_tier *memtier;
>>>> +
>>>> +	pgdat = NODE_DATA(node);
>>>> +	if (!pgdat)
>>>> +		return false;
>>>> +
>>>> +	rcu_read_lock();
>>>> +	memtier = rcu_dereference(pgdat->memtier);
>>>> +	if (!memtier) {
>>>> +		toptier = true;
>>>> +		goto out;
>>>> +	}
>>>> +	if (memtier->adistance_start >= top_tier_adistance)
>>>> +		toptier = true;
>>>> +	else
>>>> +		toptier = false;
>>>> +out:
>>>> +	rcu_read_unlock();
>>>> +	return toptier;
>>>> +}
>>>> +
>>>>  void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
>>>>  {
>>>>  	struct memory_tier *memtier;
>>>> @@ -315,6 +341,22 @@ static void establish_demotion_targets(void)
>>>>  			}
>>>>  		} while (1);
>>>>  	}
>>>> +	/*
>>>> +	 * Promotion is allowed from a memory tier to higher
>>>> +	 * memory tier only if the memory tier doesn't include
>>>> +	 * compute. We want to  skip promotion from a memory tier,
>>>> +	 * if any node that is  part of the memory tier have CPUs.
>>>> +	 * Once we detect such a memory tier, we consider that tier
>>>> +	 * as top tiper from which promotion on is not allowed.
>>>> +	 */
>>>> +	list_for_each_entry(memtier, &memory_tiers, list) {
>>>> +		tier_nodes = get_memtier_nodemask(memtier);
>>>> +		nodes_and(tier_nodes, node_states[N_CPU], tier_nodes);
>>>> +		if (!nodes_empty(tier_nodes)) {
>>>> +			top_tier_adistance = memtier->adistance_start;
>>>
>>> IMHO, this should be,
>>>
>>> 			top_tier_adistance = memtier->adistance_start + MEMTIER_CHUNK_SIZE;
>>>
>> 
>> Good catch. Will update. BTW i did send v12 version of the patchset already to the list. 
>> 
>>
>
> Checking this again, we consider a node top tier if the node's memtier abstract distance
> satisfy the below.  
>
> 	if (memtier->adistance_start <= top_tier_adistance)
> 		toptier = true;

I admit that this works correctly.  And I think that the following code
is even more correct conceptually.  If so, why not help the code reader
to understand it more easily?

        if (memtier->adistance_start + MEMTIER_CHUNK_SIZE <= top_tier_adistance)
                toptier = true;

Best Regards,
Huang, Ying

> With that we should be good with the current code. But I agree with you that top_tier_distance
> should cover the full range of the top memory tier.
>
> -aneesh