linux-kernel - Re: Re [patch RFC] mm/slab: introduce KZALLOC

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Date: Mon, 25 Mar 2024 12:00:49 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Przemek Kitszel <przemyslaw.kitszel@...el.com>, <jiri@...nulli.us>
CC: <42.hyeyoo@...il.com>, <akpm@...ux-foundation.org>, <cl@...ux.com>,
	<danielj@...dia.com>, <iamjoonsoo.kim@....com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, <mingo@...nel.org>,
	<penberg@...nel.org>, <peterz@...radead.org>, <rientjes@...gle.com>,
	<roman.gushchin@...ux.dev>, <vbabka@...e.cz>
Subject: Re: Re [patch RFC] mm/slab: introduce KZALLOC_FREE() cleanup-ed
 allocation macro

Przemek Kitszel wrote:
> > From: Jiri Pirko <jiri@...dia.com>
> > 
> > With introduction of __free() macro using cleanup infrastructure, it
> > will very likely become quite common to see following pattern:
> > 	type *var __free(kfree) = kzalloc(sizeof(*var), GFP_KERNEL);
> > 
> > To follow the CLASS() flow from cleanup.h, introduce a simple macro
> > KZALLOC_FREE() to wrap this over and allow the same flow.
> > 
> > Show an example usage in gpio-sim driver.
> > 
> > Signed-off-by: Jiri Pirko <jiri@...dia.com>
> > ---
> >  drivers/gpio/gpio-sim.c | 3 +--
> >  include/linux/slab.h    | 3 +++
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpio/gpio-sim.c b/drivers/gpio/gpio-sim.c
> > index c4106e37e6db..997237b3d80c 100644
> > --- a/drivers/gpio/gpio-sim.c
> > +++ b/drivers/gpio/gpio-sim.c
> > @@ -1496,8 +1496,7 @@ gpio_sim_config_make_device_group(struct config_group *group, const char *name)
> >  {
> >  	int id;
> >  
> > -	struct gpio_sim_device *dev __free(kfree) = kzalloc(sizeof(*dev),
> > -							    GFP_KERNEL);
> > +	KZALLOC_FREE(struct gpio_sim_device *, dev, GFP_KERNEL);
> >  	if (!dev)
> >  		return ERR_PTR(-ENOMEM);
> >  
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index b5f5ee8308d0..baee6acd58d3 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -711,6 +711,9 @@ static inline __alloc_size(1) void *kzalloc(size_t size, gfp_t flags)
> >  	return kmalloc(size, flags | __GFP_ZERO);
> >  }
> >  
> > +#define KZALLOC_FREE(_type, var, _gfp_t)				\
> > +	_type var __free(kfree) = kzalloc(sizeof(*var), _gfp_t)
> > +
> 
> Nice, but I would rather see this wrapper in the cleanup.h file, that have all
> of the rest of related stuff.
> 
> On top of that, I want to propose also a wrapper that is simpler in that it
> does not allocate but just assigns null, with that in mind `_FREE` part of your
> proposed name does not sound right.

No, do not hide assignments within macros

http://lore.kernel.org/r/CAHk-=whYxkfLVtBW_B-PgNqhKOAThTbfoH5CxtOTkwOB6VOt6w@mail.gmail.com

I.e. the amount of incremenal cleverness that include/linux/cleanup.h
will tolerate is low. Any helper should look like typical C.