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Date:   Mon, 18 Apr 2022 09:45:03 -0700
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     linux-mm@kvack.org, mhocko@kernel.org, akpm@linux-foundation.org,
        rientjes@google.com, yosryahmed@google.com, hannes@cmpxchg.org,
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        tim.c.chen@linux.intel.com, roman.gushchin@linux.dev,
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        heekwon.p@samsung.com, gim.jongmin@samsung.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/6] mm/migrate: export whether or not node is toptier in
 sysf
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On Mon, 18 Apr 2022, Dave Hansen wrote:

>On 4/16/22 20:49, Davidlohr Bueso wrote:
>> This allows userspace to know if the node is considered fast
>> memory (with CPUs attached to it). While this can be already
>> derived without a new file, this helps further encapsulate the
>> concept.
>
>What is userspace supposed to *do* with this, though?

This came as a scratch to my own itch. I wanted to start testing
more tiering patches overall that I see pop up, and wanted a way
to differentiate the slow vs the fast memories in order to better
configure workload(s) working set sizes beyond what is your typical
grep MemTotal /proc/meminfo. If there is a better way I'm all
for it.

>
>What does "attached" mean?

I'll rephrase.

>Isn't it just asking for trouble to add (known) redundancy to the ABI?
>It seems like a recipe for future inconsistency.

Perhaps. It was mostly about the fact that the notion of top tier
could also change as technology evolves.

Thanks,
Davidlohr