linux-kernel - Re: [EXT] Re: [RFC PATCH 0/2] Node migration between memory tiers

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Date:   Tue, 05 Dec 2023 16:51:02 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Srinivasulu Thanneeru <sthanneeru.opensrc@...ron.com>
Cc:     Michal Hocko <mhocko@...e.com>, <aneesh.kumar@...ux.ibm.com>,
        <linux-cxl@...r.kernel.org>, <linux-mm@...ck.org>,
        <dan.j.williams@...el.com>, <hannes@...xchg.org>,
        <hasanalmaruf@...com>, <haowang3@...com>,
        <gregory.price@...verge.com>, <tj@...nel.org>,
        <hezhongkun.hzk@...edance.com>, <fvdl@...gle.com>,
        <john@...alactic.com>, <emirakhur@...ron.com>,
        <vtavarespetr@...ron.com>, <Ravis.OpenSrc@...ron.com>,
        <Jonathan.Cameron@...wei.com>, <linux-kernel@...r.kernel.org>,
        <linux-api@...r.kernel.org>
Subject: Re: [EXT] Re: [RFC PATCH 0/2] Node migration between memory tiers

Srinivasulu Thanneeru <sthanneeru.opensrc@...ron.com> writes:

> On 12/4/2023 9:13 PM, Michal Hocko wrote:
>> CAUTION: EXTERNAL EMAIL. Do not click links or open attachments
>> unless you recognize the sender and were expecting this message.
>> On Fri 01-12-23 03:34:20, sthanneeru.opensrc@...ron.com wrote:
>>> From: Srinivasulu Thanneeru <sthanneeru.opensrc@...ron.com>
>>>
>>> The memory tiers feature allows nodes with similar memory types
>>> or performance characteristics to be grouped together in a
>>> memory tier. However, there is currently no provision for
>>> moving a node from one tier to another on demand.
>> Could you expand on why this is really needed/necessary? What is the
>> actual usecase?
>
> Hi Michal Hock,
>
> Following two use-cases we have observed.
> 1. It is not accurate to group similar memory types in the same tier,
>    because even similar memory types may have different speed grades.
>
> 2. Some systems boots up with CXL devices and DRAM on the same
> memory-tier, we need a way to move the CXL nodes to the correct tier
> from the user space.

I guess that you need to move all NUMA nodes with same performance
metrics together?  If so, That is why we previously proposed to place
the knob in "memory_type".

--
Best Regards,
Huang, Ying