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block: improve handling of the magic discard payload

Browse source 
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
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8
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);
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 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
*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);