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

Aneesh Kumar K V
2022-06-01T13:50:39Z

On 6/1/22 11:59 AM, Bharata B Rao wrote:
> On 5/27/2022 5:55 PM, Aneesh Kumar K.V wrote:
>> From: Jagdish Gediya <jvgediya@linux.ibm.com>
>>
>> By default, all nodes are assigned to DEFAULT_MEMORY_TIER which
>> is memory tier 1 which is designated for nodes with DRAM, so it
>> is not the right tier for dax devices.
>>
>> Set dax kmem device node's tier to MEMORY_TIER_PMEM, In future,
>> support should be added to distinguish the dax-devices which should
>> not be MEMORY_TIER_PMEM and right memory tier should be set for them.
>>
>> Signed-off-by: Jagdish Gediya <jvgediya@linux.ibm.com>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>> drivers/dax/kmem.c | 4 ++++
>> mm/migrate.c | 2 ++
>> 2 files changed, 6 insertions(+)
>>
>> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
>> index a37622060fff..991782aa2448 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/migrate.h>
>> #include "dax-private.h"
>> #include "bus.h"
>>
>> @@ -147,6 +148,9 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>>
>> dev_set_drvdata(dev, data);
>>
>> +#ifdef CONFIG_TIERED_MEMORY
>> + node_set_memory_tier(numa_node, MEMORY_TIER_PMEM);
>> +#endif
>
> 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?

Thank you for testing the patchset.
-aneesh