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

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Date:   Mon, 30 May 2022 13:50:43 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Ying Huang <ying.huang@...el.com>
CC:     Wei Xu <weixugc@...gle.com>,
        Aneesh Kumar K V <aneesh.kumar@...ux.ibm.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>,
        "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 Sun, 29 May 2022 12:31:30 +0800
Ying Huang <ying.huang@...el.com> wrote:

> On Fri, 2022-05-27 at 09:30 -0700, Wei Xu wrote:
> > 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.  
> 
> When discussed offline, Tim Chen pointed out that with the proposed
> interface, it's unconvenient to know the position of a given memory tier
> in all memory tiers.  We must sort "rank" of all memory tiers to know
> that.  "possible" file can be used for that.  Although "possible" file
> can be generated with a shell script, it's more convenient to show it
> directly.
> 
> Another way to address the issue is to add memtierN/pos for each memory
> tier as suggested by Tim.  It's readonly and will show position of
> "memtierN" in all memory tiers.  It's even better to show the relative
> postion to the default memory tier (DRAM with CPU). That is, the
> position of DRAM memory tier is 0.
> 
> Unlike memory tier device ID or rank, the position is relative and
> dynamic.

Hi,

I'm unconvinced.  This is better done with a shell script than
by adding ABI we'll have to live with for ever..

I'm no good at shell scripting but this does the job 
grep "" tier*/rank | sort -n -k 2 -t : 

tier2/rank:50
tier0/rank:100
tier1/rank:200
tier3/rank:240

I'm sure someone more knowledgeable will do it in a simpler fashion still.

Jonathan

> 
> Best Regards,
> Huang, Ying
> 
>