linux-kernel - Re: [RFC PATCH 1/2] mm/demotion: Expose memory type details via sysfs

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Date:   Fri, 26 Aug 2022 09:50:43 +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,
        Bharata B Rao <bharata@....com>
Subject: Re: [RFC PATCH 1/2] mm/demotion: Expose memory type details via sysfs

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

> This patch adds /sys/devices/virtual/memtier/ where all memory tier related
> 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
> ├── adistance

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

> ├── nodes
> ├── subsystem -> ../../../../bus/memtier
> └── uevent
>
> Since we will be using struct device to expose details via sysfs, drop struct
> kref and use struct device for refcounting the memtype.
>

Best Regards,
Huang, Ying