On 05/07/2017 10:44, Changpeng Liu wrote:
> Currently virtio-blk driver does not provide discard feature flag, so the
> filesystems which built on top of the block device will not send discard
> command. This is okay for HDD backend, but it will impact the performance
> for SSD backend.
>
> Add a feature flag VIRTIO_BLK_F_DISCARD and command VIRTIO_BLK_T_DISCARD
> to extend exist virtio-blk protocol, define 16 bytes discard descriptor
> for each discard segment, the discard segment defination aligns with
> SCSI or NVM Express protocols, virtio-blk driver will support multi-range
> discard request as well.
>
> Signed-off-by: Changpeng Liu <changpeng.liu@xxxxxxxxx>
Please include a patch for the specification. Since we are at it, I
would like to have three operations defined using the same descriptor:
- discard (SCSI UNMAP)
- write zeroes (SCSI WRITE SAME without UNMAP flag)
- write zeroes and possibly discard (SCSI WRITE SAME with UNMAP flag)
The last two can use the same command VIRTIO_BLK_T_WRITE_ZEROES, using
the reserved field as a flags field.
Paolo
> ---
> drivers/block/virtio_blk.c | 76 +++++++++++++++++++++++++++++++++++++++--
> include/uapi/linux/virtio_blk.h | 19 +++++++++++
> 2 files changed, 92 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 0297ad7..8f0c614 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -172,10 +172,52 @@ static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr,
> return virtqueue_add_sgs(vq, sgs, num_out, num_in, vbr, GFP_ATOMIC);
> }
>
> +static inline int virtblk_setup_discard(struct request *req)
> +{
> + unsigned short segments = blk_rq_nr_discard_segments(req), n = 0;
> + u32 block_size = queue_logical_block_size(req->q);
> + struct virtio_blk_discard *range;
> + struct bio *bio;
> +
> + if (block_size < 512 || !block_size)
> + return -1;
> +
> + range = kmalloc_array(segments, sizeof(*range), GFP_ATOMIC);
> + if (!range)
> + return -1;
> +
> + __rq_for_each_bio(bio, req) {
> + u64 slba = (bio->bi_iter.bi_sector << 9) / block_size;
> + u32 nlb = bio->bi_iter.bi_size / block_size;
> +
> + range[n].reserved = cpu_to_le32(0);
> + range[n].nlba = cpu_to_le32(nlb);
> + range[n].slba = cpu_to_le64(slba);
> + n++;
> + }
> +
> + if (WARN_ON_ONCE(n != segments)) {
> + kfree(range);
> + return -1;
> + }
> +
> + req->special_vec.bv_page = virt_to_page(range);
> + req->special_vec.bv_offset = offset_in_page(range);
> + req->special_vec.bv_len = sizeof(*range) * segments;
> + req->rq_flags |= RQF_SPECIAL_PAYLOAD;
> +
> + return 0;
> +}
> +
> static inline void virtblk_request_done(struct request *req)
> {
> struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
>
> + if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
> + kfree(page_address(req->special_vec.bv_page) +
> + req->special_vec.bv_offset);
> + }
> +
> switch (req_op(req)) {
> case REQ_OP_SCSI_IN:
> case REQ_OP_SCSI_OUT:
> @@ -237,6 +279,9 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> case REQ_OP_FLUSH:
> type = VIRTIO_BLK_T_FLUSH;
> break;
> + case REQ_OP_DISCARD:
> + type = VIRTIO_BLK_T_DISCARD;
> + break;
> case REQ_OP_SCSI_IN:
> case REQ_OP_SCSI_OUT:
> type = VIRTIO_BLK_T_SCSI_CMD;
> @@ -256,9 +301,15 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
>
> blk_mq_start_request(req);
>
> + if (type == VIRTIO_BLK_T_DISCARD) {
> + err = virtblk_setup_discard(req);
> + if (err)
> + return BLK_STS_IOERR;
> + }
> +
> num = blk_rq_map_sg(hctx->queue, req, vbr->sg);
> if (num) {
> - if (rq_data_dir(req) == WRITE)
> + if (rq_data_dir(req) == WRITE || type == VIRTIO_BLK_T_DISCARD)
> vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_OUT);
> else
> vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_IN);
> @@ -767,6 +818,25 @@ static int virtblk_probe(struct virtio_device *vdev)
> if (!err && opt_io_size)
> blk_queue_io_opt(q, blk_size * opt_io_size);
>
> + if (virtio_has_feature(vdev, VIRTIO_BLK_F_DISCARD)) {
> + q->limits.discard_alignment = blk_size;
> + q->limits.discard_granularity = blk_size;
> +
> + virtio_cread(vdev, struct virtio_blk_config, max_discard_seg, &v);
> + if (v)
> + blk_queue_max_discard_sectors(q, v);
> + else
> + blk_queue_max_discard_sectors(q, -1U);
> +
> + virtio_cread(vdev, struct virtio_blk_config, max_discard_num, &v);
> + if (v)
> + blk_queue_max_discard_segments(q, v);
> + else
> + blk_queue_max_discard_segments(q, 256);
> +
> + queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
> + }
> +
> virtio_device_ready(vdev);
>
> device_add_disk(&vdev->dev, vblk->disk);
> @@ -874,14 +944,14 @@ static int virtblk_restore(struct virtio_device *vdev)
> VIRTIO_BLK_F_SCSI,
> #endif
> VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
> - VIRTIO_BLK_F_MQ,
> + VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
> }
> ;
> static unsigned int features[] = {
> VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
> VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
> VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
> - VIRTIO_BLK_F_MQ,
> + VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
> };
>
> static struct virtio_driver virtio_blk = {
> diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
> index 9ebe4d9..3354cc3 100644
> --- a/include/uapi/linux/virtio_blk.h
> +++ b/include/uapi/linux/virtio_blk.h
> @@ -38,6 +38,7 @@
> #define VIRTIO_BLK_F_BLK_SIZE 6 /* Block size of disk is available*/
> #define VIRTIO_BLK_F_TOPOLOGY 10 /* Topology information is available */
> #define VIRTIO_BLK_F_MQ 12 /* support more than one vq */
> +#define VIRTIO_BLK_F_DISCARD 13 /* DISCARD command is supported */
>
> /* Legacy feature bits */
> #ifndef VIRTIO_BLK_NO_LEGACY
> @@ -86,6 +87,10 @@ struct virtio_blk_config {
>
> /* number of vqs, only available when VIRTIO_BLK_F_MQ is set */
> __u16 num_queues;
> + /* The maximum segment size (if VIRTIO_BLK_F_DISCARD) */
> + __u32 max_discard_seg;
> + /* The maximum number of segments (if VIRTIO_BLK_F_DISCARD) */
> + __u32 max_discard_num;
> } __attribute__((packed));
>
> /*
> @@ -114,6 +119,9 @@ struct virtio_blk_config {
> /* Get device ID command */
> #define VIRTIO_BLK_T_GET_ID 8
>
> +/* Discard command */
> +#define VIRTIO_BLK_T_DISCARD 16
> +
> #ifndef VIRTIO_BLK_NO_LEGACY
> /* Barrier before this op. */
> #define VIRTIO_BLK_T_BARRIER 0x80000000
> @@ -133,6 +141,17 @@ struct virtio_blk_outhdr {
> __virtio64 sector;
> };
>
> +/*
> + * Array of discard ranges for each request.
> + */
> +struct virtio_blk_discard {
> + /* start discard lba */
> + __virtio64 slba;
> + /* number of discard sectors */
> + __virtio32 nlba;
> + __virtio32 reserved;
> +};
> +
> #ifndef VIRTIO_BLK_NO_LEGACY
> struct virtio_scsi_inhdr {
> __virtio32 errors;
>
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