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

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Date: Thu, 21 Mar 2024 17:26:48 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: 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 [patch RFC] mm/slab: introduce KZALLOC_FREE() cleanup-ed allocation macro

> 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.

Most of the similar functions that define or declare something are named
DEFINE_STH...

(Please CC me on any future version, I have to go, sorry).

>  /**
>   * kzalloc_node - allocate zeroed memory from a particular memory node.
>   * @size: how many bytes of memory are required.
> -- 
> 2.44.0
> 
>