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>
diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index b037d0c..251101b 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -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);