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From: John Hubbard <jhubbard@nvidia.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>, <surenb@google.com>,
	<joaodias@google.com>, <willy@infradead.org>
Subject: Re: [PATCH v2] mm: cma: support sysfs
Date: Mon, 8 Feb 2021 22:27:24 -0800	[thread overview]
Message-ID: <7cc229f4-609c-71dd-9361-063ef1bf7c73@nvidia.com> (raw)
In-Reply-To: <YCIoHBGELFWAyfMi@kroah.com>

On 2/8/21 10:13 PM, Greg KH wrote:
> On Mon, Feb 08, 2021 at 05:57:17PM -0800, John Hubbard wrote:
>> On 2/8/21 3:36 PM, Minchan Kim wrote:
>> ...
>>>>>     	char name[CMA_MAX_NAME];
>>>>> +#ifdef CONFIG_CMA_SYSFS
>>>>> +	struct cma_stat	*stat;
>>>>
>>>> This should not be a pointer. By making it a pointer, you've added a bunch of pointless
>>>> extra code to the implementation.
>>>
>>> Originally, I went with the object lifetime with struct cma as you
>>> suggested to make code simple. However, Greg KH wanted to have
>>> release for kobj_type since it is consistent with other kboject
>>> handling.
>>
>> Are you talking about the kobj in your new struct cma_stat? That seems
>> like circular logic if so. I'm guessing Greg just wanted kobj methods
>> to be used *if* you are dealing with kobjects. That's a narrower point.
>>
>> I can't imagine that he would have insisted on having additional
>> allocations just so that kobj freeing methods could be used. :)
> 
> Um, yes, I was :)
> 
> You can not add a kobject to a structure and then somehow think you can
> just ignore the reference counting issues involved.  If a kobject is
> part of a structure then the kobject is responsible for controling the
> lifespan of the memory, nothing else can be.
> 
> So by making the kobject dynamic, you properly handle that memory
> lifespan of the object, instead of having to worry about the lifespan of
> the larger object (which the original patch was not doing.)
> 
> Does that make sense?
> 
That part makes sense, yes, thanks. The part that I'm trying to straighten
out is, why was kobject even added to the struct cma_stat in the first
place? Why not just leave .stat as a static member variable, without
a kobject in it, and done?

thanks,
-- 
John Hubbard
NVIDIA


  reply	other threads:[~2021-02-09  6:27 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-08 18:01 [PATCH v2] mm: cma: support sysfs Minchan Kim
2021-02-08 21:34 ` John Hubbard
2021-02-08 23:36   ` Minchan Kim
2021-02-09  1:57     ` John Hubbard
2021-02-09  4:19       ` Minchan Kim
2021-02-09  5:18         ` John Hubbard
2021-02-09  5:27           ` John Hubbard
2021-02-09  6:13       ` Greg KH
2021-02-09  6:27         ` John Hubbard [this message]
2021-02-09  6:34           ` John Hubbard
2021-02-09  6:56             ` Greg KH
2021-02-09 15:55               ` Minchan Kim
2021-02-09 17:49                 ` Greg KH
2021-02-09 20:11                   ` John Hubbard
2021-02-09 21:13                     ` Minchan Kim
2021-02-10  6:43                       ` Greg KH
2021-02-10  7:12                         ` Minchan Kim
2021-02-10  7:16                           ` John Hubbard
2021-02-10  7:26                             ` Greg KH
2021-02-10  7:50                               ` John Hubbard

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