linux-kernel - Re: [PATCH v3 updated] mm/demotion: Expose memory tier details via sysfs

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Date:   Fri, 02 Sep 2022 14:12:02 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
Cc:     Wei Xu <weixugc@...gle.com>, Johannes Weiner <hannes@...xchg.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        jvgediya.oss@...il.com, Bharata B Rao <bharata@....com>,
        Greg Thelen <gthelen@...gle.com>
Subject: Re: [PATCH v3 updated] mm/demotion: Expose memory tier details via
 sysfs

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

> On 9/2/22 11:10 AM, Huang, Ying wrote:
>> Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com> writes:
>> 
>>> On 9/2/22 10:39 AM, Wei Xu wrote:
>>>> On Thu, Sep 1, 2022 at 5:33 PM Huang, Ying <ying.huang@...el.com> wrote:
>>>>>
>>>>> Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com> writes:
>>>>>
>>>>>> On 9/1/22 12:31 PM, Huang, Ying wrote:
>>>>>>> "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:
>>>>>>>
>>>>>>>> This patch adds /sys/devices/virtual/memory_tiering/ where all memory tier
>>>>>>>> related details can be found. All allocated memory tiers will be listed
>>>>>>>> there as /sys/devices/virtual/memory_tiering/memory_tierN/
>>>>>>>>
>>>>>>>> The nodes which are part of a specific memory tier can be listed via
>>>>>>>> /sys/devices/virtual/memory_tiering/memory_tierN/nodes
>>>>>>>
>>>>>>> I think "memory_tier" is a better subsystem/bus name than
>>>>>>> memory_tiering.  Because we have a set of memory_tierN devices inside.
>>>>>>> "memory_tier" sounds more natural.  I know this is subjective, just my
>>>>>>> preference.
>>>>>>>
>>>
>>>
>>> I missed replying to this earlier. I will keep memory_tiering as subsystem name in v4 
>>> because we would want it to a susbsystem where all memory tiering related details can be found
>>> including memory type in the future. This is as per discussion 
>>>
>>> https://lore.kernel.org/linux-mm/CAAPL-u9TKbHGztAF=r-io3gkX7gorUunS2UfstudCWuihrA=0g@mail.gmail.com
>> 
>> I don't think that it's a good idea to mix 2 types of devices in one
>> subsystem (bus).  If my understanding were correct, that breaks the
>> driver core convention.
>> 
>
> All these are virtual devices .I am not sure i follow what you mean by 2 types of devices.
> memory_tiering is a subsystem that represents all the details w.r.t memory tiering. It shows
> details of memory tiers and can possibly contain details of different memory types .

IMHO, memory_tier and memory_type are 2 kind of devices.  They have
almost totally different attributes (sysfs file).  So, we should create
2 buses for them.  Each has its own attribute group.  "virtual" itself
isn't a subsystem.

Best Regards,
Huang, Ying