linux-kernel - Re: [PATCH v2] mmc: host: use kzalloc instead of kmalloc and memset

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Date:   Mon, 16 Dec 2019 23:32:16 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Pan Zhang <zhangpan26@...wei.com>
cc:     hushiyuan@...wei.com, ulf.hansson@...aro.org, allison@...utok.net,
        gregkh@...uxfoundation.org, tglx@...utronix.de,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mmc: host: use kzalloc instead of kmalloc and
 memset

On Tue, 17 Dec 2019, Pan Zhang wrote:

> Signed-off-by: Pan Zhang <zhangpan26@...wei.com>
> ---
>  drivers/mmc/host/vub300.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/mmc/host/vub300.c b/drivers/mmc/host/vub300.c
> index 6ced1b7..e18931d 100644
> --- a/drivers/mmc/host/vub300.c
> +++ b/drivers/mmc/host/vub300.c
> @@ -1227,12 +1227,10 @@ static void __download_offload_pseudocode(struct vub300_mmc_host *vub300,
>  	size -= 1;
>  	if (interrupt_size < size) {
>  		u16 xfer_length = roundup_to_multiple_of_64(interrupt_size);
> -		u8 *xfer_buffer = kmalloc(xfer_length, GFP_KERNEL);
> +		u8 *xfer_buffer = kzalloc(xfer_length, GFP_KERNEL);
>  		if (xfer_buffer) {
>  			int retval;
>  			memcpy(xfer_buffer, data, interrupt_size);
> -			memset(xfer_buffer + interrupt_size, 0,
> -			       xfer_length - interrupt_size);
>  			size -= interrupt_size;
>  			data += interrupt_size;
>  			retval =
> @@ -1270,12 +1268,10 @@ static void __download_offload_pseudocode(struct vub300_mmc_host *vub300,
>  	size -= 1;
>  	if (ts < size) {
>  		u16 xfer_length = roundup_to_multiple_of_64(ts);
> -		u8 *xfer_buffer = kmalloc(xfer_length, GFP_KERNEL);
> +		u8 *xfer_buffer = kzalloc(xfer_length, GFP_KERNEL);
>  		if (xfer_buffer) {
>  			int retval;
>  			memcpy(xfer_buffer, data, ts);
> -			memset(xfer_buffer + ts, 0,
> -			       xfer_length - ts);
>  			size -= ts;
>  			data += ts;
>  			retval =

I think the previous code is an optimization since the first 
interrupt_size bytes or ts bytes of xfer_buffer would otherwise 
unnecessarily be zeroed and then copied to.