linux-kernel - Re: [PATCH v1] mm/damon: add DAMON

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Date:   Fri, 30 Sep 2022 11:46:26 +0800
From:   haoxin <xhao@...ux.alibaba.com>
To:     SeongJae Park <sj@...nel.org>
Cc:     akpm@...ux-foundation.org, damon@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm/damon: add DAMON_OBJ macro

Hi SJ,

在 2022/9/22 上午12:41, SeongJae Park 写道:
> Hi Xin,
>
> On Wed, 21 Sep 2022 11:49:42 +0800 Xin Hao <xhao@...ux.alibaba.com> wrote:
>
>> In damon/sysfs.c file, we use 'container_of' macro to get
>> damon_sysfs_xxx struct instances, but i think it has a little
>> inconvenience, because we have to pass three arguments to
>> 'container_of', and the codes also look a bit long, so there i add a
>> 'DAMON_OBJ' macro, you just need to pass one arguments, then you can get
>> the right damon_sysfs_xxx struct instance.
> Thank you always for your helps and efforts, but I have some comments below.
>
>> Signed-off-by: Xin Hao <xhao@...ux.alibaba.com>
>> ---
>>   include/linux/damon.h |   7 ++
>>   mm/damon/sysfs.c      | 230 +++++++++++++++++-------------------------
>>   2 files changed, 102 insertions(+), 135 deletions(-)
>>
>> diff --git a/include/linux/damon.h b/include/linux/damon.h
>> index e7808a84675f..a3b577677caa 100644
>> --- a/include/linux/damon.h
>> +++ b/include/linux/damon.h
>> @@ -24,6 +24,13 @@ static inline unsigned long damon_rand(unsigned long l, unsigned long r)
>>   	return l + prandom_u32_max(r - l);
>>   }
>>   
>> +/*
>> + * Get damon_sysfs_xxx relative struct instance.
>> + */
>> +#define DAMON_OBJ(_type) ({						\
>> +	const typeof(((struct _type *)0)->kobj)*__mptr = (kobj);	\
>> +	(struct _type *)((char *)__mptr - offsetof(struct _type, kobj)); })
>> +
> So, this macro assumes two implicit rules.
> 1. The caller would have a relevant 'struct kobject *' variable called 'kobj',
>     and
> 2. The '_type' would have the field 'kobj'.
>
> I think the implicit rules could make some people confused, so would be better
> to be well documented.  Even though those are well documented, I think it
> cannot intuitively read by everyone.  Making the name better self-explaining
> might help, but then the length of the code would be not so different.
>
> So IMHO, this change makes the code a little bit shorter but unclear to
> understand what it does.  And at least to my humble eyes, use of
> 'container_of()' makes the code a little bit more verbose, but clear to
> understand.  I have no idea how we can make this code shorter while keeping it
> still easily understandable, and I think the level of verboseness is acceptable
> for the readability.  So Nack at the moment, sorry.

I really feel the need to do that， how about keep it in the sysfs.c 
file, and change it like this：

#define DAMON_OBJ(_struct) container_of(kobj, struct _struct, kobj)

it will feel easy to understand and made sense.

>
>
> Thanks,
> SJ
>
> [...]