Re: [RFC PATCH v2 0/2] Node migration between memory tiers

[Huang, Ying]

<sthanneeru.opensrc@xxxxxxxxxx> writes:

> From: Srinivasulu Thanneeru <sthanneeru.opensrc@xxxxxxxxxx>
>
> 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.
>
> To migrate a node to a tier, the corresponding node’s sysfs
> memtier_override is written with target tier id.
>
> Example: Move node2 to memory tier2 from its default tier(i.e 4)
>
> 1. To check current memtier of node2
> $cat  /sys/devices/system/node/node2/memtier_override
> memory_tier4
>
> 2. To migrate node2 to memory_tier2
> $echo 2 > /sys/devices/system/node/node2/memtier_override
> $cat  /sys/devices/system/node/node2/memtier_override
> memory_tier2
>
> Usecases:
>
> 1. Useful to move cxl nodes to the right tiers from userspace, when
>    the hardware fails to assign the tiers correctly based on
>    memorytypes.
>
>    On some platforms we have observed cxl memory being assigned to
>    the same tier as DDR memory. This is arguably a system firmware
>    bug, but it is true that tiers represent *ranges* of performance
>    and we believe it's important for the system operator to have
>    the ability to override bad firmware or OS decisions about tier
>    assignment as a fail-safe against potential bad outcomes.
>
> 2. Useful if we want interleave weights to be applied on memory tiers
>    instead of nodes.
> In a previous thread, Huang Ying <ying.huang@xxxxxxxxx> thought
> this feature might be useful to overcome limitations of systems
> where nodes with different bandwidth characteristics are grouped
> in a single tier.
> https://lore.kernel.org/lkml/87a5rw1wu8.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>
> =============
> Version Notes:
>
> V2 : Changed interface to memtier_override from adistance_offset.
> memtier_override was recommended by
> 1. John Groves <john@xxxxxxxxxxxxxx>
> 2. Ravi Shankar <ravis.opensrc@xxxxxxxxxx>
> 3. Brice Goglin <Brice.Goglin@xxxxxxxx>

It appears that you ignored my comments for V1 as follows ...

https://lore.kernel.org/lkml/87o7f62vur.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
https://lore.kernel.org/lkml/87jzpt2ft5.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
https://lore.kernel.org/lkml/87a5qp2et0.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

--
Best Regards,
Huang, Ying

> V1 : Introduced adistance_offset sysfs.
>
> =============
>
> Srinivasulu Thanneeru (2):
>   base/node: Add sysfs for memtier_override
>   memory tier: Support node migration between tiers
>
>  Documentation/ABI/stable/sysfs-devices-node |  7 ++
>  drivers/base/node.c                         | 47 ++++++++++++
>  include/linux/memory-tiers.h                | 11 +++
>  include/linux/node.h                        | 11 +++
>  mm/memory-tiers.c                           | 85 ++++++++++++---------
>  5 files changed, 125 insertions(+), 36 deletions(-)