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

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Message-ID: <5706f5e9-0609-98c9-a0cd-7d96336d73dd@amd.com>
Date:   Wed, 1 Jun 2022 11:59:49 +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 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)

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?

Regards,
Bharata.