> -----Original Message-----
> From: Michael S. Tsirkin [mailto:m...@redhat.com]
> Sent: Thursday, March 29, 2018 6:07 PM
> To: Liu, Changpeng <changpeng....@intel.com>
> Cc: virtualization@lists.linux-foundation.org; cav...@redhat.com;
> stefa...@redhat.com; jasow...@redhat.com; pbonz...@redhat.com;
> Wodkowski, PawelX <pawelx.wodkow...@intel.com>; Harris, James R
> <james.r.har...@intel.com>; fabio.miranda.mart...@canonical.com
> Subject: Re: [PATCH v3] virtio_blk: add DISCARD and WRIET ZEROES command
> support
>
> On Fri, Mar 30, 2018 at 08:49:34AM +0800, Changpeng Liu wrote:
> > Existing virtio-blk protocol doesn't have DISCARD/WRITE ZEROES
> > command support, this will impact the performance when using SSD
> > backend over file systems.
> >
> > The idea here is using 16 Bytes payload as one descriptor for
> > DISCARD/WRITE ZEROES command, users can put several ranges into
> > one command, for the purpose to support such feature, two feature
> > flags VIRTIO_BLK_F_DISCARD/VIRTIO_BLK_F_WRITE_ZEROES and two
> > commands VIRTIO_BLK_T_DISCARD/VIRTIO_BLK_T_WRITE_ZEROES are
> > introduced, and some parameters are added to the configuration
> > space to tell the OS the granularity of DISCARD/WRITE ZEROES
> > commands.
>
> Pls fix grammar in this comment, I am not sure what are you
> trying to say.
Okay, will add more description here.
>
> >
> > The specification change list here:
> > https://github.com/oasis-tcs/virtio-spec
>
> Which commit?
>
> > CHANGELOG:
> > v3: finalized the specification change.
>
> Changelog belongs after -- and should be complete
> including changes v1 to v2.
>
> > Signed-off-by: Changpeng Liu <changpeng....@intel.com>
> > ---
> > drivers/block/virtio_blk.c | 96
> +++++++++++++++++++++++++++++++++++++++--
> > include/uapi/linux/virtio_blk.h | 39 +++++++++++++++++
> > 2 files changed, 132 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 4a07593c..1943adb 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -172,10 +172,53 @@ 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_write_zeroes(struct request *req,
> > bool
> unmap)
> > +{
> > + unsigned short segments = blk_rq_nr_discard_segments(req), n = 0;
>
> Split on two lines pls:
> unsigned short n = 0;
>
> > + u32 block_size = queue_logical_block_size(req->q);
>
> Seems to be unused except for the sanity check below. Why?
>
> > + struct virtio_blk_discard_write_zeroes *range;
> > + struct bio *bio;
> > +
> > + if (block_size < 512 || !block_size)
>
> Why 512? And when is it 0?
Ok, actually this check is not necessary, will remove it.
>
> > + return -1;
>
> -1 isn't a normal errno code.
>
> > +
> > + range = kmalloc_array(segments, sizeof(*range), GFP_ATOMIC);
>
> This might be pretty large: with 64K segments it looks like you are
> trying to allocate ~1Mbyte with GFP_ATOMIC which is unlikely to succeed.
> Can we split this up in chunks?
This is already chunks now, if the backend can only support 1 segment, so the
number
is always 1, I can change the GFP_ATOMIC with GFP_KERNEL.
>
> > + if (!range)
> > + return -1;
> > +
> > + __rq_for_each_bio(bio, req) {
> > + u64 sector = bio->bi_iter.bi_sector;
> > + u32 num_sectors = bio->bi_iter.bi_size >> 9;
>
> why 9?
The sectors in virtio-blk protocol and Linux is expressed by 512-bytes.
>
> > +
> > + range[n].flags.unmap = cpu_to_le32(unmap);
> > + range[n].flags.reserved = cpu_to_le32(0);
> > + range[n].num_sectors = cpu_to_le32(num_sectors);
> > + range[n].sector = cpu_to_le64(sector);
>
> Isn't this causing sparse warnings?
No warning when I complied the module.
>
>
> > + n++;
> > + }
> > +
> > + if (WARN_ON_ONCE(n != segments)) {
>
> and when does this happen?
This check shouldn't happen too, will remove it.
>
> > + 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:
> > @@ -225,6 +268,7 @@ static blk_status_t virtio_queue_rq(struct
> blk_mq_hw_ctx *hctx,
> > int qid = hctx->queue_num;
> > int err;
> > bool notify = false;
> > + bool unmap = false;
> > u32 type;
> >
> > BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
> > @@ -237,6 +281,13 @@ 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_WRITE_ZEROES:
> > + type = VIRTIO_BLK_T_WRITE_ZEROES;
> > + unmap = !(req->cmd_flags & REQ_NOUNMAP);
> > + break;
> > case REQ_OP_SCSI_IN:
> > case REQ_OP_SCSI_OUT:
> > type = VIRTIO_BLK_T_SCSI_CMD;
> > @@ -256,9 +307,16 @@ static blk_status_t virtio_queue_rq(struct
> blk_mq_hw_ctx *hctx,
> >
> > blk_mq_start_request(req);
> >
> > + if (type == VIRTIO_BLK_T_DISCARD || type ==
> VIRTIO_BLK_T_WRITE_ZEROES) {
> > + err = virtblk_setup_discard_write_zeroes(req, unmap);
> > + if (err)
> > + return BLK_STS_IOERR;
>
> Does a failure actually indicate an IO error?
Good catch, BLK_STS_RESOURCE makes more sense.
>
>
> > + }
> > +
> > 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
> ||
> > + type == VIRTIO_BLK_T_WRITE_ZEROES)
> > 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);
> > @@ -777,6 +835,38 @@ 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_granularity = blk_size;
> > +
> > + virtio_cread(vdev, struct virtio_blk_config,
> discard_sector_alignment, &v);
> > + if (v)
> > + q->limits.discard_alignment = v << 9;
> > + else
> > + q->limits.discard_alignment = 0;
> > +
> > + virtio_cread(vdev, struct virtio_blk_config,
> > max_discard_sectors,
> &v);
> > + if (v)
> > + blk_queue_max_discard_sectors(q, v);
> > + else
> > + blk_queue_max_discard_sectors(q, UINT_MAX);
> > +
> > + virtio_cread(vdev, struct virtio_blk_config, max_discard_seg,
> > &v);
> > + if (v)
> > + blk_queue_max_discard_segments(q, v);
> > + else
> > + blk_queue_max_discard_segments(q, USHRT_MAX);
> > +
> > + queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
> > + }
> > +
> > + if (virtio_has_feature(vdev, VIRTIO_BLK_F_WRITE_ZEROES)) {
> > + virtio_cread(vdev, struct virtio_blk_config,
> max_write_zeroes_sectors, &v);
> > + if (v)
> > + blk_queue_max_write_zeroes_sectors(q, v);
> > + else
> > + blk_queue_max_write_zeroes_sectors(q, UINT_MAX);
> > + }
> > +
> > virtblk_update_capacity(vblk, false);
> > virtio_device_ready(vdev);
> >
> > @@ -885,14 +975,14 @@ 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,
> VIRTIO_BLK_F_WRITE_ZEROES,
> > }
> > ;
> > 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,
> VIRTIO_BLK_F_WRITE_ZEROES,
> > };
> >
> > static struct virtio_driver virtio_blk = {
> > diff --git a/include/uapi/linux/virtio_blk.h
> > b/include/uapi/linux/virtio_blk.h
> > index 9ebe4d9..78a60e6 100644
> > --- a/include/uapi/linux/virtio_blk.h
> > +++ b/include/uapi/linux/virtio_blk.h
> > @@ -38,6 +38,8 @@
> > #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 */
> > +#define VIRTIO_BLK_F_WRITE_ZEROES 14 /* WRITE ZEROES
> command is supported */
> >
> > /* Legacy feature bits */
> > #ifndef VIRTIO_BLK_NO_LEGACY
> > @@ -86,6 +88,22 @@ struct virtio_blk_config {
> >
> > /* number of vqs, only available when VIRTIO_BLK_F_MQ is set */
> > __u16 num_queues;
> > + /* The maximum discard segment size (if VIRTIO_BLK_F_DISCARD) */
> > + __u32 max_discard_sectors;
> > + /* The maximum number of discard segments (if VIRTIO_BLK_F_DISCARD)
> */
> > + __u32 max_discard_seg;
> > + /* The sector alignment for discard (if VIRTIO_BLK_F_DISCARD) */
> > + __u32 discard_sector_alignment;
> > + /* The maximum number of write zeroes sectors (if
> VIRTIO_BLK_F_WRITE_ZEROES) */
> > + __u32 max_write_zeroes_sectors;
> > + /* The maximum number of write zeroes segments (if
> VIRTIO_BLK_F_WRITE_ZEROES) */
> > + __u32 max_write_zeroes_seg;
> > + /* Device clear this bit when write zeroes command cannot result in
> > + * deallocating one or more sectors
> > + * (if VIRTIO_BLK_F_WRITE_ZEROES with unmap bit)
>
> Pls fix grammar in this comment, I am not sure what are you trying to
> say.
>
> > + */
> > + __u8 write_zeroes_may_unmap;
> > + __u8 unused1[3];
> > } __attribute__((packed));
> >
> > /*
> > @@ -114,6 +132,12 @@ struct virtio_blk_config {
> > /* Get device ID command */
> > #define VIRTIO_BLK_T_GET_ID 8
> >
> > +/* Discard command */
> > +#define VIRTIO_BLK_T_DISCARD 11
> > +
> > +/* Write zeroes command */
> > +#define VIRTIO_BLK_T_WRITE_ZEROES 13
> > +
> > #ifndef VIRTIO_BLK_NO_LEGACY
> > /* Barrier before this op. */
> > #define VIRTIO_BLK_T_BARRIER 0x80000000
> > @@ -133,6 +157,21 @@ struct virtio_blk_outhdr {
> > __virtio64 sector;
> > };
> >
> > +/*
> > + * discard/write zeroes range for each request.
> > + */
> > +struct virtio_blk_discard_write_zeroes {
> > + /* discard/write zeroes start sector */
> > + __virtio64 sector;
> > + /* number of discard/write zeroes sectors */
> > + __virtio32 num_sectors;
> > + /* valid for write zeroes command */
> > + struct {
> > + __virtio32 unmap:1;
> > + __virtio32 reserved:31;
> > + } flags;
> > +};
> > +
>
> You can't use bitmaps in portable code.
> The format differs between architectures.
>
> > #ifndef VIRTIO_BLK_NO_LEGACY
> > struct virtio_scsi_inhdr {
> > __virtio32 errors;
> > --
> > 1.9.3
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