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Subject: Re: [PATCH v7] mm: cma: support sysfs
To:     John Hubbard <jhubbard@nvidia.com>,
        Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        gregkh@linuxfoundation.org, surenb@google.com, joaodias@google.com,
        willy@infradead.org, Colin Ian King <colin.king@canonical.com>
References: <20210324205503.2132082-1-minchan@kernel.org>
 <65840bfd-4471-7c8d-ce71-c4705baf3bfe@gmail.com>
 <0ac4d495-eece-fb71-d334-a46e069b0c35@nvidia.com>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <0396987d-1331-51a0-83f4-0c49dd3e150c@gmail.com>
Date:   Thu, 25 Mar 2021 01:11:06 +0300
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25.03.2021 01:01, John Hubbard пишет:
> On 3/24/21 2:31 PM, Dmitry Osipenko wrote:
>> ...
>>> +#include <linux/kobject.h>
>>> +
>>> +struct cma_kobject {
>>> +    struct cma *cma;
>>> +    struct kobject kobj;
>>
>> If you'll place the kobj as the first member of the struct, then
>> container_of will be a no-op.
>>
> 
> However, *this does not matter*. Let's not get carried away. If
> container_of() ends up as a compile-time addition of +8, instead
> of +0, there is not going to be a visible effect in the world.
> Or do you have some perf data to the contrary?
> 
> Sometimes these kinds of things matter. But other times, they are
> just pointless to fret about, and this is once such case.

Performance is out of question here, my main point is about maintaining
a good coding style. Otherwise there is no point in not embedding kobj
into cma struct as well, IMO.