Re: [PATCH 7/7] sd: use ZERO_PAGE for WRITE_SAME payloads

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On Mon, 2017-03-20 at 16:43 -0400, Christoph Hellwig wrote:
> We're never touching the contents of the page, so save a memory
> allocation for these cases.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  drivers/scsi/sd.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index c18fe9ff1f8f..af632e350ab4 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -756,7 +756,7 @@ static int sd_setup_write_same16_cmnd(struct scsi_cmnd *cmd)
>  	u32 nr_sectors = blk_rq_sectors(rq) >> (ilog2(sdp->sector_size) - 9);
>  	u32 data_len = sdp->sector_size;
>  
> -	rq->special_vec.bv_page = alloc_page(GFP_ATOMIC | __GFP_ZERO);
> +	rq->special_vec.bv_page = ZERO_PAGE(0);
>  	if (!rq->special_vec.bv_page)
>  		return BLKPREP_DEFER;
>  	rq->special_vec.bv_offset = 0;
> @@ -785,7 +785,7 @@ static int sd_setup_write_same10_cmnd(struct scsi_cmnd *cmd, bool unmap)
>  	u32 nr_sectors = blk_rq_sectors(rq) >> (ilog2(sdp->sector_size) - 9);
>  	u32 data_len = sdp->sector_size;
>  
> -	rq->special_vec.bv_page = alloc_page(GFP_ATOMIC | __GFP_ZERO);
> +	rq->special_vec.bv_page = ZERO_PAGE(0);
>  	if (!rq->special_vec.bv_page)
>  		return BLKPREP_DEFER;
>  	rq->special_vec.bv_offset = 0;
> @@ -1256,7 +1256,8 @@ static void sd_uninit_command(struct scsi_cmnd *SCpnt)
>  {
>  	struct request *rq = SCpnt->request;
>  
> -	if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
> +	if ((rq->rq_flags & RQF_SPECIAL_PAYLOAD) &&
> +	    rq->special_vec.bv_page != ZERO_PAGE(0))
>  		__free_page(rq->special_vec.bv_page);
>  
>  	if (SCpnt->cmnd != scsi_req(rq)->cmd) {

Reviewed-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>






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