linux-kernel - Re: [PATCH v7] mm: cma: support sysfs

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Date:   Thu, 25 Mar 2021 01:11:06 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     John Hubbard <jhubbard@...dia.com>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        gregkh@...uxfoundation.org, surenb@...gle.com, joaodias@...gle.com,
        willy@...radead.org, Colin Ian King <colin.king@...onical.com>
Subject: Re: [PATCH v7] mm: cma: support sysfs

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.