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

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Date:   Tue, 10 Sep 2019 15:08:20 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Michal Hocko <mhocko@...nel.org>
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 2019/9/10 2:50, Michal Hocko wrote:
> 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.

Ok

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

It means some one need to guess the node id if the node is not
specified.

> 
>> 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

by node 0 missing, how do we know if node 0 is missing?
by node_online(0)?

> 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.

Yes, I should have mentioned that in the commit log.

I mentioned the below in the RFC, but somehow deleted when sending
V1:
"There may be explicit handling out there relying on NUMA_NO_NODE,
like in nvme_probe()."

>  
>> [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
>