Re: RFC: Memory Tiering Kernel Interfaces (v3)

From: Ying Huang <ying.huang@intel.com>
To: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Cc: Wei Xu <weixugc@google.com>,
	Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Greg Thelen <gthelen@google.com>, Yang Shi <shy828301@gmail.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Tim C Chen <tim.c.chen@intel.com>,
	Brice Goglin <brice.goglin@gmail.com>,
	Michal Hocko <mhocko@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Hesham Almatary <hesham.almatary@huawei.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Alistair Popple <apopple@nvidia.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Feng Tang <feng.tang@intel.com>, Linux MM <linux-mm@kvack.org>,
	Jagdish Gediya <jvgediya@linux.ibm.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	David Rientjes <rientjes@google.com>
Subject: Re: RFC: Memory Tiering Kernel Interfaces (v3)
Date: Tue, 31 May 2022 09:57:20 +0800	[thread overview]
Message-ID: <4456dc2520cf2d9368c320eb628e0043d59dfb2f.camel@intel.com> (raw)
In-Reply-To: <20220530135043.00001e88@Huawei.com>

On Mon, 2022-05-30 at 13:50 +0100, Jonathan Cameron wrote:
> On Sun, 29 May 2022 12:31:30 +0800
> Ying Huang <ying.huang@intel.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@linux.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.

I am OK to leave this to be added later if we found that it's useful.

Best Regards,
Huang, Ying

> Jonathan
> 
> > 
> > Best Regards,
> > Huang, Ying
> > 
> > 
> 