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

Huang, Ying
2022-08-01T05:10:54Z

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