[PATCH] nvme: set discard_alignment to zero

[Christoph Hellwig]

Adding Jens, who added this code, but it looks fine to me.

On Fri, Nov 24, 2017 at 04:30:53PM +0100, David Disseldorp wrote:
> Similar to 7c084289795b ("rbd: set discard_alignment to zero"), NVMe
> devices are currently incorrectly initialised with the block queue
> discard_alignment set to the NVMe stream alignment.
> 
> As per Documentation/ABI/testing/sysfs-block:
>   The discard_alignment parameter indicates how many bytes the beginning
>   of the device is offset from the internal allocation unit's natural
>   alignment.
> 
> Correcting the discard_alignment parameter to zero has no effect on how
> discard requests are propagated through the block layer - @alignment in
> __blkdev_issue_discard() remains zero. However, it does fix other
> consumers, such as LIO's Block Limits VPD response.
> 
> Signed-off-by: David Disseldorp <ddiss at suse.de>
> ---
>  drivers/nvme/host/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 25da74d310d1..2e224ab5c340 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -1287,7 +1287,7 @@ static void nvme_config_discard(struct nvme_ctrl *ctrl,
>  	BUILD_BUG_ON(PAGE_SIZE / sizeof(struct nvme_dsm_range) <
>  			NVME_DSM_MAX_RANGES);
>  
> -	queue->limits.discard_alignment = size;
> +	queue->limits.discard_alignment = 0;
>  	queue->limits.discard_granularity = size;
>  
>  	blk_queue_max_discard_sectors(queue, UINT_MAX);
> -- 
> 2.13.6
> 
> 
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