linux-kernel - Re: [PATCH v6 01/13] mm/demotion: Add support for explicit memory tiers

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Message-ID: <Yqc4nSEuso+YmPE7@cmpxchg.org>
Date:   Mon, 13 Jun 2022 09:16:13 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Ying Huang <ying.huang@...el.com>
Cc:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, Wei Xu <weixugc@...gle.com>,
        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>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v6 01/13] mm/demotion: Add support for explicit memory
 tiers

On Mon, Jun 13, 2022 at 01:30:08PM +0800, Ying Huang wrote:
> On Mon, 2022-06-13 at 09:01 +0530, Aneesh Kumar K V wrote:
> > On 6/13/22 8:52 AM, Ying Huang wrote:
> > > On Fri, 2022-06-10 at 19:22 +0530, Aneesh Kumar K.V wrote:
> > > > +config TIERED_MEMORY
> > > > +	def_bool NUMA
> > > > +
> > > 
> > > As Yang pointed out, why not just use CONFIG_NUMA?  I suspect the
> > > added value of CONIFIG_TIRED_MEMORY.
> > 
> > I decided to use TIERED_MEMORY to bring more clarity. It should be same 
> > now that we have moved CONFIG_MIGRATION dependencies to runtime. IMHO 
> > having CONFIG_TIERED_MEMORY is better than using CONFIG_NUMA.
> 
> I don't think CONFIG_TIERED_MEMORY bring no much value.  It's better
> to use CONFIG_NUMA directly.  But this is just my opinion.

I agree. As long as it's always built with CONFIG_NUMA, it's simply
NUMA code. Easy enough to modularize it later if somebody really wants
this to be configurable separately.