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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 <hch@lst.de> Reviewed-by: Max Gurtovoy <maxg@mellanox.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Israel Rukshin <israelr@mellanox.com> Signed-off-by: Keith Busch <kbusch@kernel.org>
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@ -28,6 +28,12 @@ extern unsigned int admin_timeout;
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#define NVME_DEFAULT_KATO 5
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#define NVME_KATO_GRACE 10
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#ifdef CONFIG_ARCH_NO_SG_CHAIN
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#define NVME_INLINE_SG_CNT 0
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#else
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#define NVME_INLINE_SG_CNT 2
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#endif
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extern struct workqueue_struct *nvme_wq;
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extern struct workqueue_struct *nvme_reset_wq;
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extern struct workqueue_struct *nvme_delete_wq;
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@ -731,7 +731,7 @@ static struct blk_mq_tag_set *nvme_rdma_alloc_tagset(struct nvme_ctrl *nctrl,
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set->reserved_tags = 2; /* connect + keep-alive */
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set->numa_node = nctrl->numa_node;
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set->cmd_size = sizeof(struct nvme_rdma_request) +
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SG_CHUNK_SIZE * sizeof(struct scatterlist);
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NVME_INLINE_SG_CNT * sizeof(struct scatterlist);
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set->driver_data = ctrl;
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set->nr_hw_queues = 1;
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set->timeout = ADMIN_TIMEOUT;
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@ -745,7 +745,7 @@ static struct blk_mq_tag_set *nvme_rdma_alloc_tagset(struct nvme_ctrl *nctrl,
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set->numa_node = nctrl->numa_node;
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set->flags = BLK_MQ_F_SHOULD_MERGE;
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set->cmd_size = sizeof(struct nvme_rdma_request) +
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SG_CHUNK_SIZE * sizeof(struct scatterlist);
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NVME_INLINE_SG_CNT * sizeof(struct scatterlist);
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set->driver_data = ctrl;
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set->nr_hw_queues = nctrl->queue_count - 1;
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set->timeout = NVME_IO_TIMEOUT;
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@ -1160,7 +1160,7 @@ static void nvme_rdma_unmap_data(struct nvme_rdma_queue *queue,
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}
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ib_dma_unmap_sg(ibdev, req->sg_table.sgl, req->nents, rq_dma_dir(rq));
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sg_free_table_chained(&req->sg_table, SG_CHUNK_SIZE);
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sg_free_table_chained(&req->sg_table, NVME_INLINE_SG_CNT);
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}
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static int nvme_rdma_set_sg_null(struct nvme_command *c)
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@ -1276,7 +1276,7 @@ static int nvme_rdma_map_data(struct nvme_rdma_queue *queue,
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req->sg_table.sgl = req->first_sgl;
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ret = sg_alloc_table_chained(&req->sg_table,
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blk_rq_nr_phys_segments(rq), req->sg_table.sgl,
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SG_CHUNK_SIZE);
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NVME_INLINE_SG_CNT);
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if (ret)
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return -ENOMEM;
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@ -1314,7 +1314,7 @@ out:
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out_unmap_sg:
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ib_dma_unmap_sg(ibdev, req->sg_table.sgl, req->nents, rq_dma_dir(rq));
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out_free_table:
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sg_free_table_chained(&req->sg_table, SG_CHUNK_SIZE);
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sg_free_table_chained(&req->sg_table, NVME_INLINE_SG_CNT);
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return ret;
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}
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