Re: [RFC PATCH v4 4/7] mm/demotion/dax/kmem: Set node's memory tier to MEMORY_TIER_PMEM

Aneesh Kumar K V
2022-06-03T09:05:09Z

On 6/2/22 12:06 PM, Bharata B Rao wrote:
> On 6/1/2022 7:19 PM, Aneesh Kumar K V wrote:
>> On 6/1/22 11:59 AM, Bharata B Rao wrote:
>>> I was experimenting with this patchset and found this behaviour.
>>> Here's what I did:
>>>
>>> Boot a KVM guest with vNVDIMM device which ends up with device_dax
>>> driver by default.
>>>
>>> Use it as RAM by binding it to dax kmem driver. It now appears as
>>> RAM with a new NUMA node that is put to memtier1 (the existing tier
>>> where DRAM already exists)
>>>
>>
>> That should have placed it in memtier2.
>>
>>> I can move it to memtier2 (MEMORY_RANK_PMEM) manually, but isn't
>>> that expected to happen automatically when a node with dax kmem
>>> device comes up?
>>>
>>
>> This can happen if we have added the same NUMA node to memtier1 before dax kmem driver initialized the pmem memory. Can you check before the above node_set_memory_tier_rank() whether the specific NUMA node is already part of any memory tier?
>
> When we reach node_set_memory_tier_rank(), node1 (that has the pmem device)
> is already part of memtier1 whose nodelist shows 0-1.
>

can you find out which code path added node1 to memtier1? Do you have
regular memory also appearing on node1?

-aneesh