block: improve handling of the magic discard payload
authorChristoph Hellwig <hch@lst.de>
Thu, 8 Dec 2016 22:20:32 +0000 (15:20 -0700)
committerJens Axboe <axboe@fb.com>
Fri, 9 Dec 2016 15:30:51 +0000 (08:30 -0700)
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>
13 files changed:
block/bio.c
block/blk-core.c
block/blk-lib.c
block/blk-merge.c
drivers/nvme/host/core.c
drivers/nvme/host/nvme.h
drivers/nvme/host/pci.c
drivers/nvme/host/rdma.c
drivers/nvme/target/loop.c
drivers/scsi/scsi_lib.c
drivers/scsi/sd.c
include/linux/bio.h
include/linux/blkdev.h

index 83db1f37fd0bfbe4ec4c64fc008fecd91e92e637..2b375020fc49bab0bfcabda4fc3d16118b5f1512 100644 (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;
 
index 4b7ec5958055a372e6edca08b849b220d35ca000..bd642a43b98b13fa95911677c60e4465e15d59e9 100644 (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 */
index 510a6fb1531822e10765184733066614b6740a36..ed89c8f4b2a0497af0e45f075e4781dbb5cf87d2 100644 (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);
index 1002afdfee99f846bfbb3833c5515bdfdc4563d7..182398cb152490d96b7e48c4fd74f11657c8e665 100644 (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;
 }
index 1b48514fbe99131c27f238970caad56ce716a9ac..3b1d6478dcfb48d37c2e8ec7b0559daf90e8cac1 100644 (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;
 }
index a3d6ffd874afb080b6915f1d194c6b75f2670d9d..bd5321441d127143b87563e5463d2944aa0c1b0e 100644 (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)
index 82b9b3f1f21d57e269f315b16dd6c361f22d6b4b..717d6ea47ee4743a6d81943374553e7694b4f36c 100644 (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;
 }
 
index b037d0cb2a7e05e87502e6a8dc8fb0d68d22d736..251101bf982f5f0a99ecf33bbeef50be2e2bf761 100644 (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);
index 57ded6b3ed8a989b6cefb526c7c3dea648980ed7..9aaa70071ae555efc6b6cc41d08cdcb7a6108cbf 100644 (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);
index 47a5c8783b894ceb5764ba22b0442fceb384343f..9a8ccff1121fb02638a4ef70b355546c2ca7a4dd 100644 (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)
index 65738b0aad367d1e0c3f850b8d5f7d019bbbfa0f..079c2d9759fb8a98c5283eea53b01b9ced80662e 100644 (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);
index b15323934a298e8e9c386f4af534176d927007f1..7cf8a6c70a3f71c5eca6100dfda8d67f10b20e3b 100644 (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;
index ebeef2b79c5adac3a26c5386e50dc7e2816eb16c..c5393766909d631a656ee73069dfa42c77950e9e 100644 (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);