[PATCH] ARM/dma-mapping: use kvzalloc for fallback memory allocation need

[PATCH] ARM/dma-mapping: use kvzalloc for fallback memory allocation need

[Deepak R Varma]

When the memory sizes are not known upfront, it is preferred to use the
kvzalloc helper function instead of direct conditional evaluation of
size and kzalloc/vzalloc fallback design. The kvzalloc helper function
in this case is more efficient as it avoids indefinite kzalloc retries
when a small memory size is needed but is unavailable.
This LWN article has further details on the advantages of using
kvzalloc in case of fallback memory allocation needs:
 	https://lwn.net/Articles/711653/

This patch proposal is based on following Coccinelle warning using the
kvmalloc.cocci semantic patch.

arch/arm/mm/dma-mapping.c:858:28-29: WARNING opportunity for kvmalloc

Signed-off-by: Deepak R Varma <drv@mailo.com>
---
Note: The patch proposal is compile tested only.

 arch/arm/mm/dma-mapping.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index c135f6e37a00..2b79af377a81 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -855,10 +855,7 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size,
 	int i = 0;
 	int order_idx = 0;

-	if (array_size <= PAGE_SIZE)
-		pages = kzalloc(array_size, GFP_KERNEL);
-	else
-		pages = vzalloc(array_size);
+	pages = kvzalloc(array_size, GFP_KERNEL);
 	if (!pages)
 		return NULL;

--
2.34.1

Re: [PATCH] ARM/dma-mapping: use kvzalloc for fallback memory allocation need

[Deepak R Varma]

On Tue, Dec 20, 2022 at 10:55:11AM +0530, Deepak R Varma wrote:
> When the memory sizes are not known upfront, it is preferred to use the
> kvzalloc helper function instead of direct conditional evaluation of
> size and kzalloc/vzalloc fallback design. The kvzalloc helper function
> in this case is more efficient as it avoids indefinite kzalloc retries
> when a small memory size is needed but is unavailable.
> This LWN article has further details on the advantages of using
> kvzalloc in case of fallback memory allocation needs:
>  	https://lwn.net/Articles/711653/
> 
> This patch proposal is based on following Coccinelle warning using the
> kvmalloc.cocci semantic patch.
> 
> arch/arm/mm/dma-mapping.c:858:28-29: WARNING opportunity for kvmalloc
> 
> Signed-off-by: Deepak R Varma <drv@mailo.com>

Hello,
May I please request a review and feedback on this patch proposal?

Thank you,
./drv

> ---
> Note: The patch proposal is compile tested only.
> 
>  arch/arm/mm/dma-mapping.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index c135f6e37a00..2b79af377a81 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -855,10 +855,7 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size,
>  	int i = 0;
>  	int order_idx = 0;
> 
> -	if (array_size <= PAGE_SIZE)
> -		pages = kzalloc(array_size, GFP_KERNEL);
> -	else
> -		pages = vzalloc(array_size);
> +	pages = kvzalloc(array_size, GFP_KERNEL);
>  	if (!pages)
>  		return NULL;
> 
> --
> 2.34.1
>