linux-kernel - Re: [PATCH v5 1/9] mm/demotion: Add support for explicit memory tiers

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Message-ID: <04c89154526444781f025043de890bba55282781.camel@intel.com>
Date:   Thu, 16 Jun 2022 13:51:42 +0800
From:   Ying Huang <ying.huang@...el.com>
To:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>,
        Wei Xu <weixugc@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Linux MM <linux-mm@...ck.org>,
        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>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v5 1/9] mm/demotion: Add support for explicit memory
 tiers

On Thu, 2022-06-16 at 10:17 +0530, Aneesh Kumar K V wrote:
> On 6/16/22 9:15 AM, Wei Xu wrote:
> > On Wed, Jun 15, 2022 at 6:11 PM Ying Huang <ying.huang@...el.com> wrote:
> > > 
> > > On Tue, 2022-06-14 at 14:56 -0400, Johannes Weiner wrote:
> > > > On Tue, Jun 14, 2022 at 01:31:37PM +0530, Aneesh Kumar K V wrote:
> 
> ....
> 
> > > As Jonathan Cameron pointed, we may need the memory tier ID to be
> > > stable if possible.  I know this isn't a easy task.  At least we can
> > > make the default memory tier (CPU local DRAM) ID stable (for example
> > > make it always 128)?  That provides an anchor for users to understand.
> > 
> > One of the motivations of introducing "rank" is to allow memory tier
> > ID to be stable, at least for the well-defined tiers such as the
> > default memory tier.  The default memory tier can be moved around in
> > the tier hierarchy by adjusting its rank position relative to other
> > tiers, but its device ID can remain the same, e.g. always 1.
> > 
> 
> With /sys/devices/system/memtier/default_tier userspace will be able query
> the default tier details.
> 

Yes.  This is a way to address the memory tier ID stability issue too. 
Anther choice is to make default_tier a symbolic link.


Best Regards,
Huang, Ying