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

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Date:   Fri, 02 Sep 2022 14:40:30 +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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
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 11:42 AM, Huang, Ying wrote:
>> 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.
>
> Considering both the details are related to memory tiering, wouldn't it be much simpler we consolidate
> them within the same subdirectory? I am still not clear why you are suggesting they need to be in different
> sysfs hierarchy.  It doesn't break any driver core convention as you mentioned earlier. 
>
> /sys/devices/virtual/memory_tiering/memory_tierN
> /sys/devices/virtual/memory_tiering/memory_typeN

I think we should add

 /sys/devices/virtual/memory_tier/memory_tierN
 /sys/devices/virtual/memory_type/memory_typeN

I don't think this is complex.  Devices of same bus/subsystem should
have mostly same attributes.  This is my understanding of driver core
convention.

Best Regards,
Huang, Ying