[RFC PATCH] nvme-pci: Move the sg table allocation/free into init/exit_request

[Baolin Wang]

Move the sg table allocation and free into the init_request() and
exit_request(), instead of allocating sg table when queuing requests,
which can benefit the IO performance.

Signed-off-by: Baolin Wang <baolin.w...@linux.alibaba.com>
---
 drivers/nvme/host/pci.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index b1d18f0..cf7c997 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -410,9 +410,25 @@ static int nvme_init_request(struct blk_mq_tag_set *set, 
struct request *req,
        iod->nvmeq = nvmeq;
 
        nvme_req(req)->ctrl = &dev->ctrl;
+
+       iod->sg = mempool_alloc(dev->iod_mempool, GFP_ATOMIC);
+       if (!iod->sg)
+               return -ENOMEM;
+
+       sg_init_table(iod->sg, NVME_MAX_SEGS);
        return 0;
 }
 
+static void nvme_exit_request(struct blk_mq_tag_set *set, struct request *req,
+                             unsigned int hctx_idx)
+{
+       struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
+       struct nvme_dev *dev = set->driver_data;
+
+       mempool_free(iod->sg, dev->iod_mempool);
+       iod->sg = NULL;
+}
+
 static int queue_irq_offset(struct nvme_dev *dev)
 {
        /* if we have more than 1 vec, admin queue offsets us by 1 */
@@ -557,8 +573,6 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct 
request *req)
                dma_pool_free(dev->prp_page_pool, addr, dma_addr);
                dma_addr = next_dma_addr;
        }
-
-       mempool_free(iod->sg, dev->iod_mempool);
 }
 
 static void nvme_print_sgl(struct scatterlist *sgl, int nents)
@@ -808,10 +822,6 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, 
struct request *req,
        }
 
        iod->dma_len = 0;
-       iod->sg = mempool_alloc(dev->iod_mempool, GFP_ATOMIC);
-       if (!iod->sg)
-               return BLK_STS_RESOURCE;
-       sg_init_table(iod->sg, blk_rq_nr_phys_segments(req));
        iod->nents = blk_rq_map_sg(req->q, req, iod->sg);
        if (!iod->nents)
                goto out;
@@ -1557,6 +1567,7 @@ static int nvme_create_queue(struct nvme_queue *nvmeq, 
int qid, bool polled)
        .complete       = nvme_pci_complete_rq,
        .init_hctx      = nvme_admin_init_hctx,
        .init_request   = nvme_init_request,
+       .exit_request   = nvme_exit_request,
        .timeout        = nvme_timeout,
 };
 
@@ -1566,6 +1577,7 @@ static int nvme_create_queue(struct nvme_queue *nvmeq, 
int qid, bool polled)
        .commit_rqs     = nvme_commit_rqs,
        .init_hctx      = nvme_init_hctx,
        .init_request   = nvme_init_request,
+       .exit_request   = nvme_exit_request,
        .map_queues     = nvme_pci_map_queues,
        .timeout        = nvme_timeout,
        .poll           = nvme_poll,
-- 
1.8.3.1