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/core.c b/drivers/nvme/host/core.c
index 1b48514..3b1d647 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;
}
