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block: improve handling of the magic discard payload 

Instead of allocating a single unused biovec for discard requests, send
them down without any payload.  Instead we allow the driver to add a
"special" payload using a biovec embedded into struct request (unioned
over other fields never used while in the driver), and overloading
the number of segments for this case.

This has a couple of advantages:

 - we don't have to allocate the bio_vec
 - the amount of special casing for discard requests in the block
   layer is significantly reduced
 - using this same scheme for other request types is trivial,
   which will be important for implementing the new WRITE_ZEROES
   op on devices where it actually requires a payload (e.g. SCSI)
 - we can get rid of playing games with the request length, as
   we'll never touch it and completions will work just fine
 - it will allow us to support ranged discard operations in the
   future by merging non-contiguous discard bios into a single
   request
 - last but not least it removes a lot of code

This patch is the common base for my WIP series for ranges discards and to
remove discard_zeroes_data in favor of always using REQ_OP_WRITE_ZEROES,
so it would be good to get it in quickly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Christoph Hellwig 2016-12-08 15:20:32 -07:00 committed by Jens Axboe
parent be07e14f96
commit f9d03f96b9
13 changed files with 76 additions and 138 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
block/bio.c
View File

@ -1840,15 +1840,7 @@ struct bio *bio_split(struct bio *bio, int sectors,
BUG_ON(sectors <= 0);
BUG_ON(sectors >= bio_sectors(bio));
/*
* Discards need a mutable bio_vec to accommodate the payload
* required by the DSM TRIM and UNMAP commands.
*/
if (bio_op(bio) == REQ_OP_DISCARD || bio_op(bio) == REQ_OP_SECURE_ERASE)
split = bio_clone_bioset(bio, gfp, bs);
else
split = bio_clone_fast(bio, gfp, bs);
split = bio_clone_fast(bio, gfp, bs);
if (!split)
return NULL;

34
block/blk-core.c
View File

@ -1475,38 +1475,6 @@ void blk_put_request(struct request *req)
}
EXPORT_SYMBOL(blk_put_request);
/**
* blk_add_request_payload - add a payload to a request
* @rq: request to update
* @page: page backing the payload
* @offset: offset in page
* @len: length of the payload.
*
* This allows to later add a payload to an already submitted request by
* a block driver. The driver needs to take care of freeing the payload
* itself.
*
* Note that this is a quite horrible hack and nothing but handling of
* discard requests should ever use it.
*/
void blk_add_request_payload(struct request *rq, struct page *page,
int offset, unsigned int len)
{
struct bio *bio = rq->bio;
bio->bi_io_vec->bv_page = page;
bio->bi_io_vec->bv_offset = offset;
bio->bi_io_vec->bv_len = len;
bio->bi_iter.bi_size = len;
bio->bi_vcnt = 1;
bio->bi_phys_segments = 1;
rq->__data_len = rq->resid_len = len;
rq->nr_phys_segments = 1;
}
EXPORT_SYMBOL_GPL(blk_add_request_payload);
bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
struct bio *bio)
{
@ -2642,6 +2610,8 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
return false;
}
WARN_ON_ONCE(req->rq_flags & RQF_SPECIAL_PAYLOAD);
req->__data_len -= total_bytes;
/* update sector only for requests with clear definition of sector */

2
block/blk-lib.c
View File

@ -80,7 +80,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
req_sects = end_sect - sector;
}
bio = next_bio(bio, 1, gfp_mask);
bio = next_bio(bio, 0, gfp_mask);
bio->bi_iter.bi_sector = sector;
bio->bi_bdev = bdev;
bio_set_op_attrs(bio, op, 0);

53
block/blk-merge.c
View File

@ -241,18 +241,13 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
if (!bio)
return 0;
/*
* This should probably be returning 0, but blk_add_request_payload()
* (Christoph!!!!)
*/
switch (bio_op(bio)) {
case REQ_OP_DISCARD:
case REQ_OP_SECURE_ERASE:
case REQ_OP_WRITE_SAME:
case REQ_OP_WRITE_ZEROES:
return 0;
case REQ_OP_WRITE_SAME:
return 1;
default:
break;
}
fbio = bio;
@ -410,39 +405,21 @@ new_segment:
*bvprv = *bvec;
}
static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
struct scatterlist *sglist, struct scatterlist **sg)
{
*sg = sglist;
sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
return 1;
}
static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
struct scatterlist *sglist,
struct scatterlist **sg)
{
struct bio_vec bvec, bvprv = { NULL };
struct bvec_iter iter;
int nsegs, cluster;
nsegs = 0;
cluster = blk_queue_cluster(q);
switch (bio_op(bio)) {
case REQ_OP_DISCARD:
case REQ_OP_SECURE_ERASE:
case REQ_OP_WRITE_ZEROES:
/*
* This is a hack - drivers should be neither modifying the
* biovec, nor relying on bi_vcnt - but because of
* blk_add_request_payload(), a discard bio may or may not have
* a payload we need to set up here (thank you Christoph) and
* bi_vcnt is really the only way of telling if we need to.
*/
if (!bio->bi_vcnt)
return 0;
/* Fall through */
case REQ_OP_WRITE_SAME:
*sg = sglist;
bvec = bio_iovec(bio);
sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
return 1;
default:
break;
}
int cluster = blk_queue_cluster(q), nsegs = 0;
for_each_bio(bio)
bio_for_each_segment(bvec, bio, iter)
@ -462,7 +439,11 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
struct scatterlist *sg = NULL;
int nsegs = 0;
if (rq->bio)
if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
else if (rq->bio)
nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
@ -495,7 +476,7 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
* Something must have been wrong if the figured number of
* segment is bigger than number of req's physical segments
*/
WARN_ON(nsegs > rq->nr_phys_segments);
WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
return nsegs;
}

17
drivers/nvme/host/core.c
View File

@ -239,8 +239,6 @@ static inline int nvme_setup_discard(struct nvme_ns *ns, struct request *req,
struct nvme_command *cmnd)
{
struct nvme_dsm_range *range;
struct page *page;
int offset;
unsigned int nr_bytes = blk_rq_bytes(req);
range = kmalloc(sizeof(*range), GFP_ATOMIC);
@ -257,17 +255,10 @@ static inline int nvme_setup_discard(struct nvme_ns *ns, struct request *req,
cmnd->dsm.nr = 0;
cmnd->dsm.attributes = cpu_to_le32(NVME_DSMGMT_AD);
req->completion_data = range;
page = virt_to_page(range);
offset = offset_in_page(range);
blk_add_request_payload(req, page, offset, sizeof(*range));
/*
* we set __data_len back to the size of the area to be discarded
* on disk. This allows us to report completion on the full amount
* of blocks described by the request.
*/
req->__data_len = nr_bytes;
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);
req->rq_flags |= RQF_SPECIAL_PAYLOAD;
return BLK_MQ_RQ_QUEUE_OK;
}

6
drivers/nvme/host/nvme.h
View File

@ -236,8 +236,10 @@ static inline unsigned nvme_map_len(struct request *rq)
static inline void nvme_cleanup_cmd(struct request *req)
{
if (req_op(req) == REQ_OP_DISCARD)
kfree(req->completion_data);
if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
kfree(page_address(req->special_vec.bv_page) +
req->special_vec.bv_offset);
}
}
static inline int nvme_error_status(u16 status)

27
drivers/nvme/host/pci.c
View File

@ -302,14 +302,14 @@ static void __nvme_submit_cmd(struct nvme_queue *nvmeq,
static __le64 **iod_list(struct request *req)
{
struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
return (__le64 **)(iod->sg + req->nr_phys_segments);
return (__le64 **)(iod->sg + blk_rq_nr_phys_segments(req));
}
static int nvme_init_iod(struct request *rq, unsigned size,
struct nvme_dev *dev)
{
struct nvme_iod *iod = blk_mq_rq_to_pdu(rq);
int nseg = rq->nr_phys_segments;
int nseg = blk_rq_nr_phys_segments(rq);
if (nseg > NVME_INT_PAGES || size > NVME_INT_BYTES(dev)) {
iod->sg = kmalloc(nvme_iod_alloc_size(dev, size, nseg), GFP_ATOMIC);
@ -339,8 +339,6 @@ static void nvme_free_iod(struct nvme_dev *dev, struct request *req)
__le64 **list = iod_list(req);
dma_addr_t prp_dma = iod->first_dma;
nvme_cleanup_cmd(req);
if (iod->npages == 0)
dma_pool_free(dev->prp_small_pool, list[0], prp_dma);
for (i = 0; i < iod->npages; i++) {
@ -510,7 +508,7 @@ static int nvme_map_data(struct nvme_dev *dev, struct request *req,
DMA_TO_DEVICE : DMA_FROM_DEVICE;
int ret = BLK_MQ_RQ_QUEUE_ERROR;
sg_init_table(iod->sg, req->nr_phys_segments);
sg_init_table(iod->sg, blk_rq_nr_phys_segments(req));
iod->nents = blk_rq_map_sg(q, req, iod->sg);
if (!iod->nents)
goto out;
@ -566,6 +564,7 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
}
}
nvme_cleanup_cmd(req);
nvme_free_iod(dev, req);
}
@ -596,20 +595,20 @@ static int nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
}
}
map_len = nvme_map_len(req);
ret = nvme_init_iod(req, map_len, dev);
ret = nvme_setup_cmd(ns, req, &cmnd);
if (ret != BLK_MQ_RQ_QUEUE_OK)
return ret;
ret = nvme_setup_cmd(ns, req, &cmnd);
map_len = nvme_map_len(req);
ret = nvme_init_iod(req, map_len, dev);
if (ret != BLK_MQ_RQ_QUEUE_OK)
goto out;
goto out_free_cmd;
if (req->nr_phys_segments)
if (blk_rq_nr_phys_segments(req))
ret = nvme_map_data(dev, req, map_len, &cmnd);
if (ret != BLK_MQ_RQ_QUEUE_OK)
goto out;
goto out_cleanup_iod;
blk_mq_start_request(req);
@ -620,14 +619,16 @@ static int nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
else
ret = BLK_MQ_RQ_QUEUE_ERROR;
spin_unlock_irq(&nvmeq->q_lock);
goto out;
goto out_cleanup_iod;
}
__nvme_submit_cmd(nvmeq, &cmnd);
nvme_process_cq(nvmeq);
spin_unlock_irq(&nvmeq->q_lock);
return BLK_MQ_RQ_QUEUE_OK;
out:
out_cleanup_iod:
nvme_free_iod(dev, req);
out_free_cmd:
nvme_cleanup_cmd(req);
return ret;
}

13
drivers/nvme/host/rdma.c
View File

@ -952,8 +952,7 @@ static int nvme_rdma_map_data(struct nvme_rdma_queue *queue,
struct nvme_rdma_request *req = blk_mq_rq_to_pdu(rq);
struct nvme_rdma_device *dev = queue->device;
struct ib_device *ibdev = dev->dev;
int nents, count;
int ret;
int count, ret;
req->num_sge = 1;
req->inline_data = false;
@ -965,16 +964,14 @@ static int nvme_rdma_map_data(struct nvme_rdma_queue *queue,
return nvme_rdma_set_sg_null(c);
req->sg_table.sgl = req->first_sgl;
ret = sg_alloc_table_chained(&req->sg_table, rq->nr_phys_segments,
req->sg_table.sgl);
ret = sg_alloc_table_chained(&req->sg_table,
blk_rq_nr_phys_segments(rq), req->sg_table.sgl);
if (ret)
return -ENOMEM;
nents = blk_rq_map_sg(rq->q, rq, req->sg_table.sgl);
BUG_ON(nents > rq->nr_phys_segments);
req->nents = nents;
req->nents = blk_rq_map_sg(rq->q, rq, req->sg_table.sgl);
count = ib_dma_map_sg(ibdev, req->sg_table.sgl, nents,
count = ib_dma_map_sg(ibdev, req->sg_table.sgl, req->nents,
rq_data_dir(rq) == WRITE ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
if (unlikely(count <= 0)) {
sg_free_table_chained(&req->sg_table, true);

4
drivers/nvme/target/loop.c
View File

@ -185,13 +185,13 @@ static int nvme_loop_queue_rq(struct blk_mq_hw_ctx *hctx,
if (blk_rq_bytes(req)) {
iod->sg_table.sgl = iod->first_sgl;
ret = sg_alloc_table_chained(&iod->sg_table,
req->nr_phys_segments, iod->sg_table.sgl);
blk_rq_nr_phys_segments(req),
iod->sg_table.sgl);
if (ret)
return BLK_MQ_RQ_QUEUE_BUSY;
iod->req.sg = iod->sg_table.sgl;
iod->req.sg_cnt = blk_rq_map_sg(req->q, req, iod->sg_table.sgl);
BUG_ON(iod->req.sg_cnt > req->nr_phys_segments);
}
blk_mq_start_request(req);

6
drivers/scsi/scsi_lib.c
View File

@ -1007,8 +1007,8 @@ static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer *sdb)
/*
* If sg table allocation fails, requeue request later.
*/
if (unlikely(sg_alloc_table_chained(&sdb->table, req->nr_phys_segments,
sdb->table.sgl)))
if (unlikely(sg_alloc_table_chained(&sdb->table,
blk_rq_nr_phys_segments(req), sdb->table.sgl)))
return BLKPREP_DEFER;
/*
@ -1040,7 +1040,7 @@ int scsi_init_io(struct scsi_cmnd *cmd)
bool is_mq = (rq->mq_ctx != NULL);
int error;
BUG_ON(!rq->nr_phys_segments);
BUG_ON(!blk_rq_nr_phys_segments(rq));
error = scsi_init_sgtable(rq, &cmd->sdb);
if (error)

24
drivers/scsi/sd.c
View File

@ -716,7 +716,6 @@ static int sd_setup_discard_cmnd(struct scsi_cmnd *cmd)
struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
sector_t sector = blk_rq_pos(rq);
unsigned int nr_sectors = blk_rq_sectors(rq);
unsigned int nr_bytes = blk_rq_bytes(rq);
unsigned int len;
int ret;
char *buf;
@ -772,24 +771,19 @@ static int sd_setup_discard_cmnd(struct scsi_cmnd *cmd)
goto out;
}
rq->completion_data = page;
rq->timeout = SD_TIMEOUT;
cmd->transfersize = len;
cmd->allowed = SD_MAX_RETRIES;
/*
* Initially __data_len is set to the amount of data that needs to be
* transferred to the target. This amount depends on whether WRITE SAME
* or UNMAP is being used. After the scatterlist has been mapped by
* scsi_init_io() we set __data_len to the size of the area to be
* discarded on disk. This allows us to report completion on the full
* amount of blocks described by the request.
*/
blk_add_request_payload(rq, page, 0, len);
ret = scsi_init_io(cmd);
rq->__data_len = nr_bytes;
rq->special_vec.bv_page = page;
rq->special_vec.bv_offset = 0;
rq->special_vec.bv_len = len;
rq->rq_flags |= RQF_SPECIAL_PAYLOAD;
rq->resid_len = len;
ret = scsi_init_io(cmd);
out:
if (ret != BLKPREP_OK)
__free_page(page);
@ -1182,8 +1176,8 @@ static void sd_uninit_command(struct scsi_cmnd *SCpnt)
{
struct request *rq = SCpnt->request;
if (req_op(rq) == REQ_OP_DISCARD)
__free_page(rq->completion_data);
if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
__free_page(rq->special_vec.bv_page);
if (SCpnt->cmnd != rq->cmd) {
mempool_free(SCpnt->cmnd, sd_cdb_pool);

3
include/linux/bio.h
View File

@ -197,8 +197,9 @@ static inline unsigned bio_segments(struct bio *bio)
switch (bio_op(bio)) {
case REQ_OP_DISCARD:
case REQ_OP_SECURE_ERASE:
case REQ_OP_WRITE_SAME:
case REQ_OP_WRITE_ZEROES:
return 0;
case REQ_OP_WRITE_SAME:
return 1;
default:
break;

15
include/linux/blkdev.h
View File

@ -120,10 +120,13 @@ typedef __u32 __bitwise req_flags_t;
#define RQF_HASHED ((__force req_flags_t)(1 << 16))
/* IO stats tracking on */
#define RQF_STATS ((__force req_flags_t)(1 << 17))
/* Look at ->special_vec for the actual data payload instead of the
bio chain. */
#define RQF_SPECIAL_PAYLOAD ((__force req_flags_t)(1 << 18))
/* flags that prevent us from merging requests: */
#define RQF_NOMERGE_FLAGS \
(RQF_STARTED | RQF_SOFTBARRIER | RQF_FLUSH_SEQ)
(RQF_STARTED | RQF_SOFTBARRIER | RQF_FLUSH_SEQ | RQF_SPECIAL_PAYLOAD)
#define BLK_MAX_CDB 16
@ -175,6 +178,7 @@ struct request {
*/
union {
struct rb_node rb_node; /* sort/lookup */
struct bio_vec special_vec;
void *completion_data;
};
@ -909,8 +913,6 @@ extern void __blk_put_request(struct request_queue *, struct request *);
extern struct request *blk_get_request(struct request_queue *, int, gfp_t);
extern void blk_rq_set_block_pc(struct request *);
extern void blk_requeue_request(struct request_queue *, struct request *);
extern void blk_add_request_payload(struct request *rq, struct page *page,
int offset, unsigned int len);
extern int blk_lld_busy(struct request_queue *q);
extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
struct bio_set *bs, gfp_t gfp_mask,
@ -1153,6 +1155,13 @@ extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fua);
extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
static inline unsigned short blk_rq_nr_phys_segments(struct request *rq)
{
if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
return 1;
return rq->nr_phys_segments;
}
extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
extern void blk_dump_rq_flags(struct request *, char *);
extern long nr_blockdev_pages(void);