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

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Message-ID: <1db561a9-6984-418d-9305-a2a5ece93696@micron.com>
Date:   Tue, 5 Dec 2023 01:26:07 +0530
From:   Srinivasulu Thanneeru <sthanneeru.opensrc@...ron.com>
To:     Michal Hocko <mhocko@...e.com>
CC:     <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>,
        <ying.huang@...el.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



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.

Regards,
Srini

> --
> Michal Hocko
> SUSE Labs