Re: [PATCH v1] mm/damon: add DAMON_OBJ macro

[haoxin]

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@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx>
> > ---
> >   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
>
> [...]