linux-kernel - Re: RFC: Memory Tiering Kernel Interfaces (v3)

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Date:   Fri, 27 May 2022 09:30:10 -0700
From:   Wei Xu <weixugc@...gle.com>
To:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
Cc:     Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Thelen <gthelen@...gle.com>,
        Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.com>,
        Brice Goglin <brice.goglin@...il.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>,
        Feng Tang <feng.tang@...el.com>, Linux MM <linux-mm@...ck.org>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: RFC: Memory Tiering Kernel Interfaces (v3)

On Fri, May 27, 2022 at 6:41 AM Aneesh Kumar K V
<aneesh.kumar@...ux.ibm.com> wrote:
>
> On 5/27/22 2:52 AM, Wei Xu wrote:
>
> >    The order of memory tiers is determined by their rank values, not by
> >    their memtier device names.
> >
> >    - /sys/devices/system/memtier/possible
> >
> >      Format: ordered list of "memtier(rank)"
> >      Example: 0(64), 1(128), 2(192)
> >
> >      Read-only.  When read, list all available memory tiers and their
> >      associated ranks, ordered by the rank values (from the highest
> >       tier to the lowest tier).
> >
>
> Did we discuss the need for this? I haven't done this in the patch
> series I sent across.

The "possible" file is only needed if we decide to hide the
directories of memtiers that have no nodes.  We can remove this
interface and always show all memtier directories to keep things
simpler.

> We do have
> /sys/devices/system/memtier/default_rank which should allow user to
> identify the default rank to which memory would get added via hotplug if
> the NUMA node is not part of any memory tier.

Sounds good to me to have it.

>
> -aneesh