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

From: "Huang, Ying" <ying.huang@intel.com>
To: Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>, Johannes Weiner <hannes@cmpxchg.org>,
	Linux MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yang Shi <shy828301@gmail.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Tim C Chen <tim.c.chen@intel.com>,
	Michal Hocko <mhocko@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Hesham Almatary <hesham.almatary@huawei.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Alistair Popple <apopple@nvidia.com>,
	Dan Williams <dan.j.williams@intel.com>,
	jvgediya.oss@gmail.com, Bharata B Rao <bharata@amd.com>,
	Greg Thelen <gthelen@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>
Subject: Re: [PATCH v3 updated] mm/demotion: Expose memory tier details via sysfs
Date: Fri, 02 Sep 2022 14:40:30 +0800	[thread overview]
Message-ID: <877d2mz3c1.fsf@yhuang6-desk2.ccr.corp.intel.com> (raw)
In-Reply-To: <2b4ddc45-74ae-27df-d973-6724f61f4e18@linux.ibm.com> (Aneesh Kumar K. V.'s message of "Fri, 2 Sep 2022 12:01:43 +0530")

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

> On 9/2/22 11:42 AM, Huang, Ying wrote:
>> Aneesh Kumar K V <aneesh.kumar@linux.ibm.com> writes:
>> 
>>> On 9/2/22 11:10 AM, Huang, Ying wrote:
>>>> Aneesh Kumar K V <aneesh.kumar@linux.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@intel.com> wrote:
>>>>>>>
>>>>>>> Aneesh Kumar K V <aneesh.kumar@linux.ibm.com> writes:
>>>>>>>
>>>>>>>> On 9/1/22 12:31 PM, Huang, Ying wrote:
>>>>>>>>> "Aneesh Kumar K.V" <aneesh.kumar@linux.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