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From:   "Huang, Ying" <ying.huang@intel.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc:     linux-mm@kvack.org, akpm@linux-foundation.org,
        Wei Xu <weixugc@google.com>, 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>,
        Johannes Weiner <hannes@cmpxchg.org>, jvgediya.oss@gmail.com,
        Bharata B Rao <bharata@amd.com>
Subject: Re: [RFC PATCH 1/2] mm/demotion: Expose memory type details via sysfs
References: <20220825092325.381517-1-aneesh.kumar@linux.ibm.com>
Date:   Fri, 26 Aug 2022 09:50:43 +0800
In-Reply-To: <20220825092325.381517-1-aneesh.kumar@linux.ibm.com> (Aneesh
        Kumar K. V.'s message of "Thu, 25 Aug 2022 14:53:24 +0530")
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"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:

> This patch adds /sys/devices/virtual/memtier/ where all memory tier relat=
ed
> details can be found. All allocated memory types will be listed there as
> /sys/devices/virtual/memtier/memtypeN/

Another choice is to make memory types and memory tiers system devices.
That is,

/sys/devices/system/memory_type/memory_typeN
/sys/devices/system/memory_tier/memory_tierN

That looks more natural to me.  Because we already have "node" and
"memory" devices there.  Why don't you put memory types and memory tiers
there?

And, I think we shouldn't put "memory_type" in the "memory_tier"
directory.  "memory_type" isn't a part of "memory_tier".

> The nodes which are part of a specific memory type can be listed via
> /sys/devices/system/memtier/memtypeN/nodes.

How about create links to /sys/devices/system/node/nodeN in
"memory_type".  But I'm OK to have "nodes" file too.

> The adistance value of a specific memory type can be listed via
> /sys/devices/system/memtier/memtypeN/adistance.
>
> A directory listing looks like:
> :/sys/devices/virtual/memtier# tree memtype1
> memtype1
> =E2=94=9C=E2=94=80=E2=94=80 adistance

Why not just use "abstract_distance"?  This is user space interface,
it's better to be intuitive.

> =E2=94=9C=E2=94=80=E2=94=80 nodes
> =E2=94=9C=E2=94=80=E2=94=80 subsystem -> ../../../../bus/memtier
> =E2=94=94=E2=94=80=E2=94=80 uevent
>
> Since we will be using struct device to expose details via sysfs, drop st=
ruct
> kref and use struct device for refcounting the memtype.
>

Best Regards,
Huang, Ying