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Message-ID: <8e651a1e-d189-3e8a-438f-298f21402bd2@linux.ibm.com>
Date:   Wed, 1 Jun 2022 19:19:58 +0530
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Subject: Re: [RFC PATCH v4 4/7] mm/demotion/dax/kmem: Set node's memory tier
 to MEMORY_TIER_PMEM
Content-Language: en-US
To:     Bharata B Rao <bharata@amd.com>, linux-mm@kvack.org,
        akpm@linux-foundation.org
Cc:     Huang Ying <ying.huang@intel.com>,
        Greg Thelen <gthelen@google.com>,
        Yang Shi <shy828301@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Tim C Chen <tim.c.chen@intel.com>,
        Brice Goglin <brice.goglin@gmail.com>,
        Michal Hocko <mhocko@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Hesham Almatary <hesham.almatary@huawei.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Alistair Popple <apopple@nvidia.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Feng Tang <feng.tang@intel.com>,
        Jagdish Gediya <jvgediya@linux.ibm.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        David Rientjes <rientjes@google.com>
References: <CAAPL-u-dFp7PwPH6DfbYdnY8xaGsHz3tRQ0CPGVkiqURvdN8=A@mail.gmail.com>
 <20220527122528.129445-1-aneesh.kumar@linux.ibm.com>
 <20220527122528.129445-5-aneesh.kumar@linux.ibm.com>
 <5706f5e9-0609-98c9-a0cd-7d96336d73dd@amd.com>
From:   Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>
In-Reply-To: <5706f5e9-0609-98c9-a0cd-7d96336d73dd@amd.com>
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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