[PATCH] block: improve handling of the magic discard payload
Christoph Hellwig
hch at lst.de
Fri Dec 2 04:19:02 PST 2016
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 at lst.de>
---
block/bio.c | 10 +--------
block/blk-core.c | 34 ++---------------------------
block/blk-lib.c | 2 +-
block/blk-merge.c | 53 +++++++++++++++-------------------------------
drivers/nvme/host/core.c | 17 ++++-----------
drivers/nvme/host/nvme.h | 6 ++++--
drivers/nvme/host/pci.c | 27 +++++++++++------------
drivers/nvme/host/rdma.c | 13 +++++-------
drivers/nvme/target/loop.c | 4 ++--
drivers/scsi/scsi_lib.c | 6 +++---
drivers/scsi/sd.c | 24 ++++++++-------------
include/linux/bio.h | 3 ++-
include/linux/blkdev.h | 15 ++++++++++---
13 files changed, 76 insertions(+), 138 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index 83db1f3..2b37502 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -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;
diff --git a/block/blk-core.c b/block/blk-core.c
index 3f2eb8d..bb9934a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -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)
{
@@ -2641,6 +2609,8 @@ 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 */
diff --git a/block/blk-lib.c b/block/blk-lib.c
index 510a6fb..ed89c8f 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -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);
diff --git a/block/blk-merge.c b/block/blk-merge.c
index cf2848c..5f719d3 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -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;
}
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 525d653..aa75b71 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -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;
}
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index a3d6ffd..bd53214 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -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)
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 8e179cf..90b0568 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -303,14 +303,14 @@ 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);
@@ -340,8 +340,6 @@ 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++) {
@@ -511,7 +509,7 @@ 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;
@@ -567,6 +565,7 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
}
}
+ nvme_cleanup_cmd(req);
nvme_free_iod(dev, req);
}
@@ -597,20 +596,20 @@ 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;
cmnd.common.command_id = req->tag;
blk_mq_start_request(req);
@@ -622,14 +621,16 @@ 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;
}
diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index 6d102f9..042e319 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -964,8 +964,7 @@ 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;
@@ -977,16 +976,14 @@ 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);
diff --git a/drivers/nvme/target/loop.c b/drivers/nvme/target/loop.c
index be56d05..79c5d7c 100644
--- a/drivers/nvme/target/loop.c
+++ b/drivers/nvme/target/loop.c
@@ -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);
}
iod->cmd.common.command_id = req->tag;
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 47a5c87..9a8ccff 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -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)
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 65738b0..079c2d9 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -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);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index b153239..7cf8a6c 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -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;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ebeef2b..c539376 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -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);
--
2.1.4
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