nvme-fc: Avoid preallocating big SGL for data (b1ae1a23) · Commits · 戴 / test

nvme_fc_create_io_queues() 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-fc, 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. Reviewed-by:

Max Gurtovoy <maxg@mellanox.com> Reviewed-by:

James Smart <james.smart@broadcom.com> Signed-off-by:

Israel Rukshin <israelr@mellanox.com> Signed-off-by:

Keith Busch <kbusch@kernel.org>

drivers/nvme/host/fc.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -95,7 +95,7 @@ struct nvme_fc_fcp_op {

		struct nvme_fcp_op_w_sgl {
		struct nvme_fc_fcp_op op;
		struct scatterlist sgl[SG_CHUNK_SIZE];
		struct scatterlist sgl[NVME_INLINE_SG_CNT];
		uint8_t priv[0];
		};

		@@ -2141,7 +2141,7 @@ nvme_fc_map_data(struct nvme_fc_ctrl ctrl, struct request rq,
		freq->sg_table.sgl = freq->first_sgl;
		ret = sg_alloc_table_chained(&freq->sg_table,
		blk_rq_nr_phys_segments(rq), freq->sg_table.sgl,
		SG_CHUNK_SIZE);
		NVME_INLINE_SG_CNT);
		if (ret)
		return -ENOMEM;

		@@ -2150,7 +2150,7 @@ nvme_fc_map_data(struct nvme_fc_ctrl ctrl, struct request rq,
		freq->sg_cnt = fc_dma_map_sg(ctrl->lport->dev, freq->sg_table.sgl,
		op->nents, rq_dma_dir(rq));
		if (unlikely(freq->sg_cnt <= 0)) {
		sg_free_table_chained(&freq->sg_table, SG_CHUNK_SIZE);
		sg_free_table_chained(&freq->sg_table, NVME_INLINE_SG_CNT);
		freq->sg_cnt = 0;
		return -EFAULT;
		}
		@@ -2173,7 +2173,7 @@ nvme_fc_unmap_data(struct nvme_fc_ctrl ctrl, struct request rq,
		fc_dma_unmap_sg(ctrl->lport->dev, freq->sg_table.sgl, op->nents,
		rq_dma_dir(rq));

		sg_free_table_chained(&freq->sg_table, SG_CHUNK_SIZE);
		sg_free_table_chained(&freq->sg_table, NVME_INLINE_SG_CNT);

		freq->sg_cnt = 0;
		}

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