linux-kernel - Re: [PATCH 2/4] memory-hotplug: add node_device

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Date:	Mon, 1 Oct 2012 15:54:40 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	<wency@...fujitsu.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <rientjes@...gle.com>,
	<liuj97@...il.com>, <len.brown@...el.com>,
	<benh@...nel.crashing.org>, <paulus@...ba.org>,
	<minchan.kim@...il.com>, <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] memory-hotplug: add node_device_release

Hi Kosaki-san,

2012/09/29 7:19, KOSAKI Motohiro wrote:
>>>> I don't understand it. How can we get rid of the warning?
>>>
>>> See cpu_device_release() for example.
>>
>> If we implement a function like cpu_device_release(), the warning
>> disappears. But the comment says in the function "Never copy this way...".
>> So I think it is illegal way.
>
> What does "illegal" mean?

The "illegal" means the code should not be mimicked.

> You still haven't explain any benefit of your code. If there is zero
> benefit, just kill it.
> I believe everybody think so.
>
> Again, Which benefit do you have?

The patch has a benefit to delets a warning message.

>
>>>>> Why do we need this node_device_release() implementation?
>>>>
>>>> I think that this is a manner of releasing object related kobject.
>>>
>>> No.  Usually we never call memset() from release callback.
>>
>> What we want to release is a part of array, not a pointer.
>> Therefore, there is only this way instead of kfree().
>
> Why? Before your patch, we don't have memset() and did work it.

If we does not apply the patch, a warning message is shown.
So I think it did not work well.

> I can't understand what mean "only way".

For deleting a warning message, I created a node_device_release().
In the manner of releasing kobject, the function frees a object related
to the kobject. So most functions calls kfree() for releasing it.
In node_device_release(), we need to free a node struct. If the node
struct is pointer, I can free it by kfree. But the node struct is a part
of node_devices[] array. I cannot free it. So I filled the node struct
with 0.

But you think it is not good. Do you have a good solution?

Thanks,
Yasuaki Ishimatsu

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