linux-kernel - Re: [PATCH v4] Documentation, dt, numa: Add note to empty NUMA node

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Message-ID: <20210625070217.4ffmfe7nwlusbbjc@gator>
Date:   Fri, 25 Jun 2021 09:02:17 +0200
From:   Andrew Jones <drjones@...hat.com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        rdunlap@...radead.org, robh+dt@...nel.org, shan.gavin@...il.com
Subject: Re: [PATCH v4] Documentation, dt, numa: Add note to empty NUMA node

On Fri, Jun 25, 2021 at 01:23:38PM +0800, Gavin Shan wrote:
> The empty memory nodes, where no memory resides in, are allowed.
> For these empty memory nodes, the 'len' of 'reg' property is zero.
> The NUMA node IDs are still valid and parsed, but memory can be
> added to them through hotplug afterwards. I finds difficulty to
> get where it's properly documented.
> 
> So lets add note to empty memory nodes in the NUMA binding doc.
> 
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>  Documentation/devicetree/bindings/numa.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/numa.txt b/Documentation/devicetree/bindings/numa.txt
> index 21b35053ca5a..0fc882e44270 100644
> --- a/Documentation/devicetree/bindings/numa.txt
> +++ b/Documentation/devicetree/bindings/numa.txt
> @@ -109,6 +109,10 @@ Example:
>  Dual socket system consists of 2 boards connected through ccn bus and
>  each board having one socket/soc of 8 cpus, memory and pci bus.
>  
> +Note that empty memory nodes, which no memory resides in, are allowed.
> +The NUMA node IDs in these empty memory nodes are still valid, but
> +memory can be added into them through hotplug afterwards.

Please change the second sentence to:

  The NUMA node IDs in these empty memory nodes are still valid and
  memory may be added into them through hotplug afterwards.

But, this doesn't look like the right place for this paragraph. You're
adding the paragraph to the example section, but the example doesn't have
any empty memory nodes.

I think the paragraph should be added to section "2 - numa-node-id" and an
example empty memory node should be provided. Also, the commit message
talks about the length of 'reg' being zero, which is an important
distinction which should also be documented.

Thanks,
drew

> +
>  	memory@...000 {
>  		device_type = "memory";
>  		reg = <0x0 0xc00000 0x0 0x80000000>;
> -- 
> 2.23.0
>