Message-ID: <20210625101821.3t3vgj2pnw3hqpzm@gator>
Date:   Fri, 25 Jun 2021 12:18:21 +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 06:36:48PM +1000, Gavin Shan wrote:
> On 6/25/21 5:06 PM, Andrew Jones wrote:
> > On Fri, Jun 25, 2021 at 09:02:17AM +0200, Andrew Jones wrote:
> > > 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
> > 
> > Or maybe even create a new section for it.
> > 
> > > 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.
> > > 
> 
> Drew, thanks for your comments. Yeah, it sounds sensible to create
> a new section for it and an example would be more helpful. Please
> check if below changes are fine to you. I probably need Randy's review
> again.
> 
> I'm trying to avoid too many revisions for this sort of trivial patch,
> even though I already had. However, it's time frame for v5.14 and I'm
> pushing this to be merged during the cycle.

We must revise until we're satisfied... Also, I wouldn't call writing
specifications trivial.

> 
> --- a/Documentation/devicetree/bindings/numa.txt
> +++ b/Documentation/devicetree/bindings/numa.txt
> @@ -103,7 +103,65 @@ Example:
>  		};
>  ==============================================================================
> -4 - Example dts
> +4 - Empty memory node

nodes

> +==============================================================================
> +
> +Empty memory nodes, which no memory resides in, are allowed. The 'length'
> +field of 'reg' property is zero, but 'base-address' is dummy and invalid

 is a dummy address and is invalid.

> +for these empty memory nodes.

Can drop this "for these empty memory nodes" that's clear from the
context.

> However, the NUMA node IDs and distance maps
> +for them are still valid, but memory may be added into them through hotplug
   ^ drop 'for them'         ^ Again, this should be "and". "but" is a
contrastive conjunction. We want to express that the nodes are valid *and*
may have memory hotplugged later.

> +afterwards.

I'll just rewrite it:

 Empty memory nodes, which no memory resides in, are allowed. The 'length'
 field of the 'reg' property is zero, but the 'base-address' is a dummy
 address and invalid. However, the NUMA node IDs and distance maps are
 still valid and memory may be added into them through hotplug afterwards.

> +
> +Example:
> +
> +	memory@0 {
> +		device_type = "memory";
> +		reg = <0x0 0x0 0x0 0x80000000>;
> +		numa-node-id = <0>;
> +	};
> +
> +	memory@...0000000 {
> +		device_type = "memory";
> +		reg = <0x0 0x80000000 0x0 0x80000000>;
> +		numa-node-id = <1>;
> +	};
> +
> +	/* Empty memory node */

You should write how you've selected the dummy addresses for the empty
memory nodes, perhaps here in the /* Empty memory node */ comments or
above in the paragraph or both.

> +	memory@...00000000 {
> +		device_type = "memory";
> +		reg = <0x1 0x0 0x0 0x0>;
> +		numa-node-id = <2>;
> +	};
> +
> +	/* Empty memory node */
> +	memory@...80000000 {
> +		device_type = "memory";
> +		reg = <0x1 0x80000000 0x0 0x0>;
> +		numa-node-id = <3>;
> +	};
> +
> +	distance-map {
> +		compatible = "numa-distance-map-v1";
> +		distance-matrix = <0 0  10>,
> +				  <0 1  20>,
> +				  <0 2  40>,
> +				  <0 3  20>,
> +				  <1 0  20>,
> +				  <1 1  10>,
> +				  <1 2  20>,
> +				  <1 3  40>,
> +				  <2 0  40>,
> +				  <2 1  20>,
> +				  <2 2  10>,
> +				  <2 3  20>,
> +				  <3 0  20>,
> +				  <3 1  40>,
> +				  <3 2  20>,
> +				  <3 3  10>;
> +	};
> +
> +==============================================================================
> +5 - Example dts
>  ==============================================================================
>  Dual socket system consists of 2 boards connected through ccn bus and
> 
> 
> Thanks,
> Gavin
> 
>

Thanks,
drew

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