From 38e1800275d3af607e4df92ff49dc2cf442586a4 Mon Sep 17 00:00:00 2001 From: Israel Rukshin Date: Sun, 24 Nov 2019 18:38:30 +0200 Subject: nvme-rdma: Avoid preallocating big SGL for data nvme_rdma_alloc_tagset() preallocates a big buffer for the IO SGL based on SG_CHUNK_SIZE. Modern DMA engines are often capable of dealing with very big segments so the SG_CHUNK_SIZE is often too big. SG_CHUNK_SIZE results in a static 4KB SGL allocation per command. If a controller has lots of deep queues, preallocation for the sg list can consume substantial amounts of memory. For nvme-rdma, nr_hw_queues can be 128 and each queue's depth 128. This means the resulting preallocation for the data SGL is 128*128*4K = 64MB per controller. Switch to runtime allocation for SGL for lists longer than 2 entries. This is the approach used by NVMe PCI so it should be reasonable for NVMeOF as well. Runtime SGL allocation has always been the case for the legacy I/O path so this is nothing new. The preallocated small SGL depends on SG_CHAIN so if the ARCH doesn't support SG_CHAIN, use only runtime allocation for the SGL. We didn't notice of a performance degradation, since for small IOs we'll use the inline SG and for the bigger IOs the allocation of a bigger SGL from slab is fast enough. Suggested-by: Christoph Hellwig Reviewed-by: Max Gurtovoy Reviewed-by: Christoph Hellwig Signed-off-by: Israel Rukshin Signed-off-by: Keith Busch --- drivers/nvme/host/nvme.h | 6 ++++++ drivers/nvme/host/rdma.c | 10 +++++----- 2 files changed, 11 insertions(+), 5 deletions(-) (limited to 'drivers/nvme') diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h index 3b9cbe0668fa..1024fec7914c 100644 --- a/drivers/nvme/host/nvme.h +++ b/drivers/nvme/host/nvme.h @@ -28,6 +28,12 @@ extern unsigned int admin_timeout; #define NVME_DEFAULT_KATO 5 #define NVME_KATO_GRACE 10 +#ifdef CONFIG_ARCH_NO_SG_CHAIN +#define NVME_INLINE_SG_CNT 0 +#else +#define NVME_INLINE_SG_CNT 2 +#endif + extern struct workqueue_struct *nvme_wq; extern struct workqueue_struct *nvme_reset_wq; extern struct workqueue_struct *nvme_delete_wq; diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c index dce59459ed41..2a47c6c5007e 100644 --- a/drivers/nvme/host/rdma.c +++ b/drivers/nvme/host/rdma.c @@ -731,7 +731,7 @@ static struct blk_mq_tag_set *nvme_rdma_alloc_tagset(struct nvme_ctrl *nctrl, set->reserved_tags = 2; /* connect + keep-alive */ set->numa_node = nctrl->numa_node; set->cmd_size = sizeof(struct nvme_rdma_request) + - SG_CHUNK_SIZE * sizeof(struct scatterlist); + NVME_INLINE_SG_CNT * sizeof(struct scatterlist); set->driver_data = ctrl; set->nr_hw_queues = 1; set->timeout = ADMIN_TIMEOUT; @@ -745,7 +745,7 @@ static struct blk_mq_tag_set *nvme_rdma_alloc_tagset(struct nvme_ctrl *nctrl, set->numa_node = nctrl->numa_node; set->flags = BLK_MQ_F_SHOULD_MERGE; set->cmd_size = sizeof(struct nvme_rdma_request) + - SG_CHUNK_SIZE * sizeof(struct scatterlist); + NVME_INLINE_SG_CNT * sizeof(struct scatterlist); set->driver_data = ctrl; set->nr_hw_queues = nctrl->queue_count - 1; set->timeout = NVME_IO_TIMEOUT; @@ -1160,7 +1160,7 @@ static void nvme_rdma_unmap_data(struct nvme_rdma_queue *queue, } ib_dma_unmap_sg(ibdev, req->sg_table.sgl, req->nents, rq_dma_dir(rq)); - sg_free_table_chained(&req->sg_table, SG_CHUNK_SIZE); + sg_free_table_chained(&req->sg_table, NVME_INLINE_SG_CNT); } static int nvme_rdma_set_sg_null(struct nvme_command *c) @@ -1276,7 +1276,7 @@ static int nvme_rdma_map_data(struct nvme_rdma_queue *queue, req->sg_table.sgl = req->first_sgl; ret = sg_alloc_table_chained(&req->sg_table, blk_rq_nr_phys_segments(rq), req->sg_table.sgl, - SG_CHUNK_SIZE); + NVME_INLINE_SG_CNT); if (ret) return -ENOMEM; @@ -1314,7 +1314,7 @@ out: out_unmap_sg: ib_dma_unmap_sg(ibdev, req->sg_table.sgl, req->nents, rq_dma_dir(rq)); out_free_table: - sg_free_table_chained(&req->sg_table, SG_CHUNK_SIZE); + sg_free_table_chained(&req->sg_table, NVME_INLINE_SG_CNT); return ret; } -- cgit v1.2.3