Re: [PATCH] dma: map_benchmark: turn dma_sg_map_param buf into a flexible array

[Qinxin Xia <xiaqinxin@huawei.com>]

在 2026/5/26 6:06, Rosen Penev 写道:
> The buf pointer was kmalloc_array()'d immediately after the parent
> struct allocation, with the count (granule, validated to 1..1024 by
> the ioctl) trivially available beforehand.  Move buf to the struct
> tail as a flexible array member and fold the two allocations into a
> single kzalloc_flex(), dropping the kfree(params->buf) in both the
> prepare error path and unprepare.
> 
> Add __counted_by for extra runtime analysis.
> 
> Assisted-by: Claude:Opus-4.7
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>   kernel/dma/map_benchmark.c | 29 +++++++++++++----------------
>   1 file changed, 13 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/dma/map_benchmark.c b/kernel/dma/map_benchmark.c
> index 29eeb5fdf199..a65da5c7710c 100644
> --- a/kernel/dma/map_benchmark.c
> +++ b/kernel/dma/map_benchmark.c
> @@ -121,35 +121,35 @@ static struct map_benchmark_ops dma_single_map_benchmark_ops = {
>   struct dma_sg_map_param {
>   	struct sg_table sgt;
>   	struct device *dev;
> -	void **buf;
>   	u32 npages;
>   	u32 dma_dir;
> +	void *buf[] __counted_by(npages);
>   };
>   
>   static void *dma_sg_map_benchmark_prepare(struct map_benchmark_data *map)
>   {
> +	struct dma_sg_map_param *params;
>   	struct scatterlist *sg;
> +	u32 npages;
>   	int i;
>   
> -	struct dma_sg_map_param *params = kzalloc(sizeof(*params), GFP_KERNEL);
> -
> -	if (!params)
> -		return NULL;
>   	/*
>   	 * Set the number of scatterlist entries based on the granule.
>   	 * In SG mode, 'granule' represents the number of scatterlist entries.
>   	 * Each scatterlist entry corresponds to a single page.
>   	 */
> -	params->npages = map->bparam.granule;
> +	npages = map->bparam.granule;
> +
> +	params = kzalloc_flex(*params, buf, npages);
> +	if (!params)
> +		return NULL;
> +
> +	params->npages = npages;
>   	params->dma_dir = map->bparam.dma_dir;
>   	params->dev = map->dev;
> -	params->buf = kmalloc_array(params->npages, sizeof(*params->buf),
> -				    GFP_KERNEL);
> -	if (!params->buf)
> -		goto out;
>   
> -	if (sg_alloc_table(&params->sgt, params->npages, GFP_KERNEL))
> -		goto free_buf;
> +	if (sg_alloc_table(&params->sgt, npages, GFP_KERNEL))
> +		goto free_params;
>   
>   	for_each_sgtable_sg(&params->sgt, sg, i) {
>   		params->buf[i] = (void *)__get_free_page(GFP_KERNEL);
> @@ -166,9 +166,7 @@ static void *dma_sg_map_benchmark_prepare(struct map_benchmark_data *map)
>   		free_page((unsigned long)params->buf[i]);
>   
>   	sg_free_table(&params->sgt);
> -free_buf:
> -	kfree(params->buf);
> -out:
> +free_params:
>   	kfree(params);
>   	return NULL;
>   }
> @@ -183,7 +181,6 @@ static void dma_sg_map_benchmark_unprepare(void *mparam)
>   
>   	sg_free_table(&params->sgt);
>   
> -	kfree(params->buf);
>   	kfree(params);
>   }
>   

Thanks for the patch.

Sorry for the delay — your email was unfortunately flagged as phishing
and almost missed. I suspect the issue was the Cc list containing
descriptive text.

It's a nice clean code.
I've tested it on Kunpeng 920, and it looks good.
Feel free to add my Reviewed-by:
Reviewed-by: Qinxin Xia <xiaqinxin@huawei.com>

-- 
Thanks,
Qinxin