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

Bharata B Rao
2022-06-06T10:15:53Z

On 6/3/2022 2:34 PM, Aneesh Kumar K V wrote:
> 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?

node_set_memory_tier_rank+0x63/0x80
migrate_on_reclaim_callback+0x40/0x4d
blocking_notifier_call_chain+0x68/0x90
memory_notify+0x1b/0x20
online_pages+0x257/0x2f0
memory_subsys_online+0x99/0x150
device_online+0x65/0x90
online_memory_block+0x1b/0x20
walk_memory_blocks+0x85/0xc0
? generic_online_page+0x40/0x40
add_memory_resource+0x1fa/0x2d0
add_memory_driver_managed+0x80/0xc0
dev_dax_kmem_probe+0x1af/0x250
dax_bus_probe+0x6e/0xa0

After this the explicit call to node_set_memory_tier_rank(numa_node, MEMORY_RANK_PMEM)
from dev_dax_kmem_probe() finds that the memtier is already set.

> Do you have regular memory also appearing on node1?

No, regular memory is on Node0.

Regards,
Bharata.