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

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Date:   Wed, 1 Jun 2022 19:19:58 +0530
From:   Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To:     Bharata B Rao <bharata@....com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org
Cc:     Huang Ying <ying.huang@...el.com>,
        Greg Thelen <gthelen@...gle.com>,
        Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.com>,
        Brice Goglin <brice.goglin@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Feng Tang <feng.tang@...el.com>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [RFC PATCH v4 4/7] mm/demotion/dax/kmem: Set node's memory tier
 to MEMORY_TIER_PMEM

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@...ux.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@...ux.ibm.com>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.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