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:   Thu, 2 Jun 2022 12:06:25 +0530
From:   Bharata B Rao <bharata@....com>
To:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.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 6/1/2022 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.

Regards,
Bharata.