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

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Date:   Tue, 21 Jun 2022 13:57:52 +0530
From:   Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tim C Chen <tim.c.chen@...el.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Wei Xu <weixugc@...gle.com>, Huang Ying <ying.huang@...el.com>,
        Greg Thelen <gthelen@...gle.com>,
        Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        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 6/14/22 10:15 PM, Jonathan Cameron wrote:
> 

...

>>
>> It could be simple tier0, tier1, tier2 numbering again, but the
>> numbers now would mean something to the user. A rank tunable is no
>> longer necessary.
> 
> This feels like it might make tier assignments a bit less stable
> and hence run into question of how to hook up accounting. Not my
> area of expertise though, but it was put forward as one of the reasons
> we didn't want hotplug to potentially end up shuffling other tiers
> around.  The desire was for a 'stable' entity.  Can avoid that with
> 'space' between them but then we sort of still have rank, just in a
> form that makes updating it messy (need to create a new tier to do
> it).
> 
>>

How about we do what is proposed here 

https://lore.kernel.org/linux-mm/7b72ccf4-f4ae-cb4e-f411-74d055482026@linux.ibm.com

The cgroup accounting patch posted here https://lore.kernel.org/linux-mm/cover.1655242024.git.tim.c.chen@linux.intel.com

looks at top tier accounting per cgroup and I am not sure what tier ID stability is expected
for top tier accounting. 

-aneesh