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

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Message-ID: <87o7f62vur.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Mon, 04 Dec 2023 16:52:12 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     <sthanneeru.opensrc@...ron.com>
Cc:     <aneesh.kumar@...ux.ibm.com>, <hannes@...xchg.org>,
        <hasanalmaruf@...com>, <haowang3@...com>,
        <gregory.price@...verge.com>, <dan.j.williams@...el.com>,
        <mhocko@...e.com>, <tj@...nel.org>, <hezhongkun.hzk@...edance.com>,
        <fvdl@...gle.com>, <john@...alactic.com>, <mirakhur@...ron.com>,
        <vtavarespetr@...ron.com>, <Ravis.OpenSrc@...ron.com>,
        <Jonathan.Cameron@...wei.com>, <linux-kernel@...r.kernel.org>,
        <linux-api@...r.kernel.org>, Johannes Weiner <hannes@...xchg.org>
Subject: Re: [RFC PATCH 0/2] Node migration between memory tiers

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

> 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.
>
> This patch series aims to support node migration between tiers
> on demand by sysadmin/root user using the provided sysfs for
> node migration. Each tier has a start abstract distance(adistance)
> and range.

We have discussed migrating nodes (in fact nodes of a memory type)
between tiers by sysadmin/root before.  The basic idea comes from
Johannes.  It is summarized in page 11 of [1],

[1] https://lpc.events/event/16/contributions/1209/attachments/1042/1995/Live%20In%20a%20World%20With%20Multiple%20Memory%20Types.pdf

The abstract distance of a memory type (e.g., GPU HBM) can be adjusted
via a sysfs knob (<memory_type>/abstract_distance_offset).

I still think that the memory type is better to be used to change
the abstract distance of nodes.  Do you agree?

--
Best Regards,
Huang, Ying

> To migrate a node to a tier, the corresponding node’s sysfs
> adistance_offset is written with a value corresponding to
> the tier’s adistance.
>
> Example: Move node2 to memory tier5 from its default tier(i.e 4)
>
> 1. Check default values:
> $cat /sys/devices/virtual/memory_tiering/memory_tier4/nodelist
> 0-2
>
> $cat /sys/devices/system/node/node0/adistance_offset
> 0
> $cat /sys/devices/system/node/node1/adistance_offset
> 0
> $cat /sys/devices/system/node/node2/adistance_offset
> 0
>
> 2. Move node2 to  tier5:
>
> To move node2 from emory_tier4 (adistance=512) to
> emory_tier5 (abstract=640), set the `adistance_offset` of
> node 2 to 128 (i.e., 512 + 128 = 640).
>
> Tier4 adistance start can be derved from tier-id
> (i.e for tier4, 4 << 7 = 512).
>
> $echo 128 > /sys/devices/system/node/node2/adistance_offset
> $cat /sys/devices/system/node/node2/adistance_offset
> 128
>
> 3. Verify node2's tier id:
>
> $cat /sys/devices/virtual/memory_tiering/memory_tier5/nodelist
> 2
> $cat /sys/devices/virtual/memory_tiering/memory_tier4/nodelist
> 0-1
>
> Srinivasulu Thanneeru (2):
>   base/node: Add sysfs for adistance_offset
>   memory tier: Support node migration between tiers
>
>  drivers/base/node.c          | 51 +++++++++++++++++++++++
>  include/linux/memory-tiers.h | 11 +++++
>  include/linux/node.h         |  6 +++
>  mm/memory-tiers.c            | 79 ++++++++++++++++++++----------------
>  4 files changed, 113 insertions(+), 34 deletions(-)