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

Huang, Ying
2022-08-01T06:37:31Z

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

> 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.

Can we use node_memory_types[] to indicate whether a node is managed by
a driver?

Regardless being succeeded or failed, dev_dax_kmem_remove() will set
node_memory_types[] = NULL. But until node is offlined, we will still
keep the node in the memory_dev_type (dax_pmem_type).

And we will prevent dax/kmem from unloading via try_module_get() and add
"struct module *" to struct memory_dev_type.

Best Regards,
Huang, Ying

> 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;
>
> [back