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

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Date:   Tue, 1 Nov 2022 15:34:51 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     "Huang, Ying" <ying.huang@...el.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

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?) ?

Thanks!

-- 
Michal Hocko
SUSE Labs