linux-kernel - Re: [PATCH] driver core: ensure a device has valid node id in device

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Date:   Mon, 9 Sep 2019 20:50:35 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     gregkh@...uxfoundation.org, rafael@...nel.org,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...nel.org, linuxarm@...wei.com
Subject: Re: [PATCH] driver core: ensure a device has valid node id in
 device_add()

On Mon 09-09-19 14:04:23, Yunsheng Lin wrote:
> Currently a device does not belong to any of the numa nodes
> (dev->numa_node is NUMA_NO_NODE) when the node id is neither
> specified by fw nor by virtual device layer and the device has
> no parent device.
> 
> According to discussion in [1]:

Please do not reference important parts of the justification via a link.
Just quote the relevant part to the changelog. It is just too easy that
external links die - not to mention lkml.org.

> Even if a device's numa node is not specified, the device really
> does belong to a node.

What does this mean?

> This patch sets the device node to node 0 in device_add() if the
> device's node id is not specified and it either has no parent
> device, or the parent device also does not have a valid node id.

Why is node 0 special? I have seen platforms with node 0 missing or
being memory less. The changelog also lacks an actual problem
descripton. Why do we even care about NUMA_NO_NODE? E.g. the page
allocator interprets NUMA_NO_NODE as the closest node with a memory.
And by closest it really means to the CPU which is performing the
allocation.
 
> [1] https://lkml.org/lkml/2019/9/2/466
> 
> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
> ---
> Changelog RFC -> v1:
> 1. Drop log error message and use a "if" instead of "? :".
> 2. Drop the RFC tag.
> ---
>  drivers/base/core.c  | 10 +++++++---
>  include/linux/numa.h |  2 ++
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 1669d41..f79ad20 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2107,9 +2107,13 @@ int device_add(struct device *dev)
>  	if (kobj)
>  		dev->kobj.parent = kobj;
>  
> -	/* use parent numa_node */
> -	if (parent && (dev_to_node(dev) == NUMA_NO_NODE))
> -		set_dev_node(dev, dev_to_node(parent));
> +	/* use parent numa_node or default node 0 */
> +	if (!numa_node_valid(dev_to_node(dev))) {
> +		if (parent && numa_node_valid(dev_to_node(parent)))
> +			set_dev_node(dev, dev_to_node(parent));
> +		else
> +			set_dev_node(dev, 0);
> +	}
>  
>  	/* first, register with generic layer. */
>  	/* we require the name to be set before, and pass NULL */
> diff --git a/include/linux/numa.h b/include/linux/numa.h
> index 110b0e5..eccc757 100644
> --- a/include/linux/numa.h
> +++ b/include/linux/numa.h
> @@ -13,4 +13,6 @@
>  
>  #define	NUMA_NO_NODE	(-1)
>  
> +#define numa_node_valid(node)	((unsigned int)(node) < nr_node_ids)
> +
>  #endif /* _LINUX_NUMA_H */
> -- 
> 2.8.1

-- 
Michal Hocko
SUSE Labs