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

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Date:	Mon, 1 Oct 2012 14:12:13 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...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

On Mon, Oct 1, 2012 at 2:54 AM, Yasuaki Ishimatsu
<isimatu.yasuaki@...fujitsu.com> wrote:
> 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?

Do nothing. just add empty release function and kill a warning.
Obviously do nothing can't make any performance drop nor any
side effect.

meaningless memset() is just silly from point of cache pollution view.
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