linux-kernel - Re: [RFC] memory tiering: use small chunk size and more tiers

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Date:   Wed, 02 Nov 2022 08:39:49 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Bharata B Rao <bharata@....com>,
        Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Jagdish Gediya <jvgediya.oss@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Tim Chen <tim.c.chen@...el.com>, Wei Xu <weixugc@...gle.com>,
        Yang Shi <shy828301@...il.com>
Subject: Re: [RFC] memory tiering: use small chunk size and more tiers

Michal Hocko <mhocko@...e.com> writes:

> On Mon 31-10-22 09:33:49, Huang, Ying wrote:
> [...]
>> In the upstream implementation, 4 tiers are possible below DRAM.  That's
>> enough for now.  But in the long run, it may be better to define more.
>> 100 possible tiers below DRAM may be too extreme.
>
> I am just curious. Is any configurations with more than couple of tiers
> even manageable? I mean applications have been struggling even with
> regular NUMA systems for years and vast majority of them is largerly
> NUMA unaware. How are they going to configure for a more complex system
> when a) there is no resource access control so whatever you aim for
> might not be available and b) in which situations there is going to be a
> demand only for subset of tears (GPU memory?) ?

Sorry for confusing.  I think that there are only several (less than 10)
tiers in a system in practice.  Yes, here, I suggested to define 100 (10
in the later text) POSSIBLE tiers below DRAM.  My intention isn't to
manage a system with tens memory tiers.  Instead, my intention is to
avoid to put 2 memory types into one memory tier by accident via make
the abstract distance range of each memory tier as small as possible.
More possible memory tiers, smaller abstract distance range of each
memory tier.

Best Regards,
Huang, Ying