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

Aneesh Kumar K V
2022-08-01T05:39:12Z

On 8/1/22 10:40 AM, Huang, Ying wrote:
> 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().
>

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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