linux-kernel - Re: [PATCH v13 4/9] mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX

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Date:   Wed, 10 Aug 2022 09:09:07 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Wei Xu <weixugc@...gle.com>, Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.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>,
        Johannes Weiner <hannes@...xchg.org>, jvgediya.oss@...il.com
Subject: Re: [PATCH v13 4/9] mm/demotion/dax/kmem: Set node's abstract
 distance to MEMTIER_DEFAULT_DAX_ADISTANCE

Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com> writes:

> On 8/9/22 8:34 AM, Huang, Ying wrote:
>> "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:
>> 
>>> By default, all nodes are assigned to the default memory tier which
>>> is the memory tier designated for nodes with DRAM
>>>
>>> Set dax kmem device node's tier to slower memory tier by assigning
>>> abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE. Low-level drivers
>>> like papr_scm or ACPI NFIT can initialize memory device type to a
>>> more accurate value based on device tree details or HMAT.
>> 
>> I don't know how ACPI NFIT can help here.  Can you teach me?
>> 
>> Per my understanding, we may use the information provided by ACPI SLIT
>> or HMAT (or device tree via papr_scm) to create memory types.  Before
>> that is implemented, we just create a memory type with default abstract
>> distance.
>> 
>
> My idea is to use ACPI NFIT driver that creates a persistent memory region
> (nvdimm_region_create) to also create memory type and assign that to the
> NUMA node mapping that region. For now NFIT driver manages all the persistent
> memory region/DIMM creation (drivers/acpi/nfit/core.c). It can also do the
> memory type creation using other ACPI information like SLIT/HMAT etc. Similarly
> CXL driver can do the same using CDAT.

I still think that it's better to create memory types in dax/kmem.c and
CXL driver.  But we can discuss further on that later.

Best Regards,
Huang, Ying