linux-kernel - Re: [PATCH] thermal: sysfs: fall back to vzalloc for cooling device's statistics

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Date:   Mon, 24 Aug 2020 12:40:35 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Yue Hu <zbestahu@...il.com>, rui.zhang@...el.com,
        amit.kucheria@...durent.com, viresh.kumar@...aro.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        huyue2@...ong.com, zbestahu@....com
Subject: Re: [PATCH] thermal: sysfs: fall back to vzalloc for cooling device's
 statistics

On 18/08/2020 08:30, Yue Hu wrote:
> From: Yue Hu <huyue2@...ong.com>
> 
> We observed warning about kzalloc() when register thermal cooling device
> in backlight_device_register(). backlight display can be a cooling device
> since reducing screen brightness will can help reduce temperature.
> 
> However, ->get_max_state of backlight will assign max brightness of 1024
> to states. The memory size can be getting 1MB+ due to states * states.

What are the benefits of a 1024 states cooling device ? Is the
difference noticeable with a such small step ?


> That is so large to trigger kmalloc() warning.
> 
> So, let's remove it and try vzalloc() if kzalloc() fails.
> 
> Signed-off-by: Yue Hu <huyue2@...ong.com>
> ---
>  drivers/thermal/thermal_sysfs.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index aa99edb..9bae0b6 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -16,6 +16,8 @@
>  #include <linux/device.h>
>  #include <linux/err.h>
>  #include <linux/slab.h>
> +#include <linux/vmalloc.h>
> +#include <linux/mm.h>
>  #include <linux/string.h>
>  #include <linux/jiffies.h>
>  
> @@ -919,7 +921,9 @@ static void cooling_device_stats_setup(struct thermal_cooling_device *cdev)
>  	var += sizeof(*stats->time_in_state) * states;
>  	var += sizeof(*stats->trans_table) * states * states;
>  
> -	stats = kzalloc(var, GFP_KERNEL);
> +	stats = kzalloc(var, GFP_KERNEL | __GFP_NOWARN);
> +	if (!stats)
> +		stats = vzalloc(var);
>  	if (!stats)
>  		return;
>  
> @@ -938,7 +942,7 @@ static void cooling_device_stats_setup(struct thermal_cooling_device *cdev)
>  
>  static void cooling_device_stats_destroy(struct thermal_cooling_device *cdev)
>  {
> -	kfree(cdev->stats);
> +	kvfree(cdev->stats);
>  	cdev->stats = NULL;
>  }
>  
> 


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