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Subject: [RFC PATCH 0/2] Node migration between memory tiers
Date:   Fri, 1 Dec 2023 03:34:20 +0530
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From: Srinivasulu Thanneeru <sthanneeru.opensrc@micron.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.

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(-)

-- 
2.25.1