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nvme-fc: Avoid preallocating big SGL for data 

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>
This commit is contained in:
Israel Rukshin 2019-11-24 18:38:31 +02:00 committed by Keith Busch
parent 38e1800275
commit b1ae1a2389
1 changed files with 4 additions and 4 deletions
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8
drivers/nvme/host/fc.c
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@ -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;
}