From: Israel Rukshin <israelr@mellanox.com>
Date: Sun, 24 Nov 2019 18:38:32 +0200
Subject: [PATCH] nvmet-loop: Avoid preallocating big SGL for data
Git-commit: 52e6d8ed16fdf9f1d2923a2b036222a5ac834b1d
Patch-mainline: v5.5-rc2
References: bsc#1175995,jsc#SLE-15608
nvme_loop_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 nvmet-loop, 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.
Tested-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Acked-by: Hannes Reinecke <hare@suse.com>
---
drivers/nvme/target/loop.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/nvme/target/loop.c b/drivers/nvme/target/loop.c
index a758bb3d5dd4..4df4ebde208a 100644
--- a/drivers/nvme/target/loop.c
+++ b/drivers/nvme/target/loop.c
@@ -76,7 +76,7 @@ static void nvme_loop_complete_rq(struct request *req)
{
struct nvme_loop_iod *iod = blk_mq_rq_to_pdu(req);
- sg_free_table_chained(&iod->sg_table, SG_CHUNK_SIZE);
+ sg_free_table_chained(&iod->sg_table, NVME_INLINE_SG_CNT);
nvme_complete_rq(req);
}
@@ -156,7 +156,7 @@ static blk_status_t nvme_loop_queue_rq(struct blk_mq_hw_ctx *hctx,
iod->sg_table.sgl = iod->first_sgl;
if (sg_alloc_table_chained(&iod->sg_table,
blk_rq_nr_phys_segments(req),
- iod->sg_table.sgl, SG_CHUNK_SIZE)) {
+ iod->sg_table.sgl, NVME_INLINE_SG_CNT)) {
nvme_cleanup_cmd(req);
return BLK_STS_RESOURCE;
}
@@ -342,7 +342,7 @@ static int nvme_loop_configure_admin_queue(struct nvme_loop_ctrl *ctrl)
ctrl->admin_tag_set.reserved_tags = 2; /* connect + keep-alive */
ctrl->admin_tag_set.numa_node = NUMA_NO_NODE;
ctrl->admin_tag_set.cmd_size = sizeof(struct nvme_loop_iod) +
- SG_CHUNK_SIZE * sizeof(struct scatterlist);
+ NVME_INLINE_SG_CNT * sizeof(struct scatterlist);
ctrl->admin_tag_set.driver_data = ctrl;
ctrl->admin_tag_set.nr_hw_queues = 1;
ctrl->admin_tag_set.timeout = ADMIN_TIMEOUT;
@@ -516,7 +516,7 @@ static int nvme_loop_create_io_queues(struct nvme_loop_ctrl *ctrl)
ctrl->tag_set.numa_node = NUMA_NO_NODE;
ctrl->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
ctrl->tag_set.cmd_size = sizeof(struct nvme_loop_iod) +
- SG_CHUNK_SIZE * sizeof(struct scatterlist);
+ NVME_INLINE_SG_CNT * sizeof(struct scatterlist);
ctrl->tag_set.driver_data = ctrl;
ctrl->tag_set.nr_hw_queues = ctrl->ctrl.queue_count - 1;
ctrl->tag_set.timeout = NVME_IO_TIMEOUT;
--
2.16.4