linux-kernel - Re: [PATCH 0/2] Implement numa node notifier

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Message-ID: <78c976ba-1eaf-47b7-a310-b8a99a3882e2@suse.cz>
Date: Wed, 2 Apr 2025 18:06:51 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Oscar Salvador <osalvador@...e.de>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Hyeonggon Yoo <42.hyeyoo@...il.com>,
 mkoutny@...e.com, Dan Williams <dan.j.williams@...el.com>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH 0/2] Implement numa node notifier

On 4/1/25 11:27, Oscar Salvador wrote:
> Memory notifier is a tool that allow consumers to get notified whenever
> memory gets onlined or offlined in the system.
> Currently, there are 10 consumers of that, but 5 out of those 10 consumers
> are only interested in getting notifications when a numa node has changed its
> state.
> That means going from memoryless to memory-aware of vice versa.
> 
> Which means that for every {online,offline}_pages operation they get
> notified even though the numa node might not have changed its state.
> 
> The first patch implements a numa node notifier that does just that, and have
> those consumers register in there, so they get notified only when they are
> interested.

What if we had two chains:

register_node_notifier()
register_node_normal_notifier()

I think they could have shared the state #defines and struct node_notify
would have just one nid and be always >= 0.

Or would it add too much extra boilerplate and only slab cares?

> The second patch replaces 'status_change_normal{_normal}' fields within
> memory_notify with a 'nid', as that is only what we need for memory
> notifer and update the only user of it (page_ext).
> 
> Consumers that are only interested in numa node states change are:
> 
>  - memory-tier
>  - slub
>  - cpuset
>  - hmat
>  - cxl
> 
> 
> Oscar Salvador (2):
>   mm,memory_hotplug: Implement numa node notifier
>   mm,memory_hotplug: Replace status_change_nid parameter in
>     memory_notify
> 
>  drivers/acpi/numa/hmat.c  |  6 +--
>  drivers/base/node.c       | 19 +++++++++
>  drivers/cxl/core/region.c | 14 +++----
>  drivers/cxl/cxl.h         |  4 +-
>  include/linux/memory.h    | 37 ++++++++++++++++++
>  kernel/cgroup/cpuset.c    |  2 +-
>  mm/memory-tiers.c         |  8 ++--
>  mm/memory_hotplug.c       | 82 +++++++++++++++++++++++++++++----------
>  mm/page_ext.c             | 12 +-----
>  mm/slub.c                 | 22 +++++------
>  10 files changed, 146 insertions(+), 60 deletions(-)
>