[RFC PATCH 6/7] nvme-pci: use a better encoding for small prp pool allocations

[Leon Romanovsky <leon@kernel.org>]

From: Christoph Hellwig <hch@lst.de>

There is plenty of unused space in the iod next to nr_descriptors.
Add a separate bool (which could be condensed to a single bit once we
start running out of space) to encode that the transfer is using
the full page sized pool, and use a normal 0..n count for the number of
descriptors.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 drivers/nvme/host/pci.c | 85 +++++++++++++++++++----------------------
 1 file changed, 40 insertions(+), 45 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index ba077a42cbba..79cd65a5f311 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -45,6 +45,7 @@
 #define NVME_MAX_SEGS	128
 
 #define NVME_MAX_NR_DESCRIPTORS		5
+#define NVME_SMALL_DESCRIPTOR_SIZE	256
 
 static int use_threaded_interrupts;
 module_param(use_threaded_interrupts, int, 0444);
@@ -224,8 +225,8 @@ struct nvme_iod {
 	struct nvme_request req;
 	struct nvme_command cmd;
 	bool aborted;
-	/* # of PRP/SGL descriptors: (0 for small pool) */
-	s8 nr_descriptors;
+	u8 nr_descriptors;	/* # of PRP/SGL descriptors */
+	bool large_descriptors;	/* uses the full page sized descriptor pool */
 	unsigned int dma_len;	/* length of single DMA segment mapping */
 	dma_addr_t first_dma;
 	dma_addr_t meta_dma;
@@ -514,13 +515,27 @@ static inline bool nvme_pci_use_sgls(struct nvme_dev *dev, struct request *req,
 	return true;
 }
 
-static void nvme_free_prps(struct nvme_dev *dev, struct request *req)
+static inline struct dma_pool *nvme_dma_pool(struct nvme_dev *dev,
+		struct nvme_iod *iod)
+{
+	if (iod->large_descriptors)
+		return dev->prp_page_pool;
+	return dev->prp_small_pool;
+}
+
+static void nvme_free_descriptors(struct nvme_dev *dev, struct request *req)
 {
 	const int last_prp = NVME_CTRL_PAGE_SIZE / sizeof(__le64) - 1;
 	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
 	dma_addr_t dma_addr = iod->first_dma;
 	int i;
 
+	if (iod->nr_descriptors == 1) {
+		dma_pool_free(nvme_dma_pool(dev, iod), iod->descriptors[0],
+				dma_addr);
+		return;
+	}
+
 	for (i = 0; i < iod->nr_descriptors; i++) {
 		__le64 *prp_list = iod->descriptors[i];
 		dma_addr_t next_dma_addr = le64_to_cpu(prp_list[last_prp]);
@@ -543,15 +558,7 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
 	WARN_ON_ONCE(!iod->sgt.nents);
 
 	dma_unmap_sgtable(dev->dev, &iod->sgt, rq_dma_dir(req), 0);
-
-	if (iod->nr_descriptors == 0)
-		dma_pool_free(dev->prp_small_pool, iod->descriptors[0],
-			      iod->first_dma);
-	else if (iod->nr_descriptors == 1)
-		dma_pool_free(dev->prp_page_pool, iod->descriptors[0],
-			      iod->first_dma);
-	else
-		nvme_free_prps(dev, req);
+	nvme_free_descriptors(dev, req);
 	mempool_free(iod->sgt.sgl, dev->iod_mempool);
 }
 
@@ -573,7 +580,6 @@ static blk_status_t nvme_pci_setup_prps(struct nvme_dev *dev,
 		struct request *req, struct nvme_rw_command *cmnd)
 {
 	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
-	struct dma_pool *pool;
 	int length = blk_rq_payload_bytes(req);
 	struct scatterlist *sg = iod->sgt.sgl;
 	int dma_len = sg_dma_len(sg);
@@ -581,7 +587,7 @@ static blk_status_t nvme_pci_setup_prps(struct nvme_dev *dev,
 	int offset = dma_addr & (NVME_CTRL_PAGE_SIZE - 1);
 	__le64 *prp_list;
 	dma_addr_t prp_dma;
-	int nprps, i;
+	int i;
 
 	length -= (NVME_CTRL_PAGE_SIZE - offset);
 	if (length <= 0) {
@@ -603,27 +609,23 @@ static blk_status_t nvme_pci_setup_prps(struct nvme_dev *dev,
 		goto done;
 	}
 
-	nprps = DIV_ROUND_UP(length, NVME_CTRL_PAGE_SIZE);
-	if (nprps <= (256 / 8)) {
-		pool = dev->prp_small_pool;
-		iod->nr_descriptors = 0;
-	} else {
-		pool = dev->prp_page_pool;
-		iod->nr_descriptors = 1;
-	}
+	if (DIV_ROUND_UP(length, NVME_CTRL_PAGE_SIZE) >
+	    NVME_SMALL_DESCRIPTOR_SIZE / sizeof(__le64))
+		iod->large_descriptors = true;
 
-	prp_list = dma_pool_alloc(pool, GFP_ATOMIC, &prp_dma);
-	if (!prp_list) {
-		iod->nr_descriptors = -1;
+	prp_list = dma_pool_alloc(nvme_dma_pool(dev, iod), GFP_ATOMIC,
+			&prp_dma);
+	if (!prp_list)
 		return BLK_STS_RESOURCE;
-	}
-	iod->descriptors[0] = prp_list;
+	iod->descriptors[iod->nr_descriptors++] = prp_list;
 	iod->first_dma = prp_dma;
 	i = 0;
 	for (;;) {
 		if (i == NVME_CTRL_PAGE_SIZE >> 3) {
 			__le64 *old_prp_list = prp_list;
-			prp_list = dma_pool_alloc(pool, GFP_ATOMIC, &prp_dma);
+
+			prp_list = dma_pool_alloc(dev->prp_page_pool,
+					GFP_ATOMIC, &prp_dma);
 			if (!prp_list)
 				goto free_prps;
 			iod->descriptors[iod->nr_descriptors++] = prp_list;
@@ -650,7 +652,7 @@ static blk_status_t nvme_pci_setup_prps(struct nvme_dev *dev,
 	cmnd->dptr.prp2 = cpu_to_le64(iod->first_dma);
 	return BLK_STS_OK;
 free_prps:
-	nvme_free_prps(dev, req);
+	nvme_free_descriptors(dev, req);
 	return BLK_STS_RESOURCE;
 bad_sgl:
 	WARN(DO_ONCE(nvme_print_sgl, iod->sgt.sgl, iod->sgt.nents),
@@ -679,7 +681,6 @@ static blk_status_t nvme_pci_setup_sgls(struct nvme_dev *dev,
 		struct request *req, struct nvme_rw_command *cmd)
 {
 	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
-	struct dma_pool *pool;
 	struct nvme_sgl_desc *sg_list;
 	struct scatterlist *sg = iod->sgt.sgl;
 	unsigned int entries = iod->sgt.nents;
@@ -694,21 +695,13 @@ static blk_status_t nvme_pci_setup_sgls(struct nvme_dev *dev,
 		return BLK_STS_OK;
 	}
 
-	if (entries <= (256 / sizeof(struct nvme_sgl_desc))) {
-		pool = dev->prp_small_pool;
-		iod->nr_descriptors = 0;
-	} else {
-		pool = dev->prp_page_pool;
-		iod->nr_descriptors = 1;
-	}
+	if (entries > NVME_SMALL_DESCRIPTOR_SIZE / sizeof(*sg_list))
+		iod->large_descriptors = true;
 
-	sg_list = dma_pool_alloc(pool, GFP_ATOMIC, &sgl_dma);
-	if (!sg_list) {
-		iod->nr_descriptors = -1;
+	sg_list = dma_pool_alloc(nvme_dma_pool(dev, iod), GFP_ATOMIC, &sgl_dma);
+	if (!sg_list)
 		return BLK_STS_RESOURCE;
-	}
-
-	iod->descriptors[0] = sg_list;
+	iod->descriptors[iod->nr_descriptors++] = sg_list;
 	iod->first_dma = sgl_dma;
 
 	nvme_pci_sgl_set_seg(&cmd->dptr.sgl, sgl_dma, entries);
@@ -834,7 +827,8 @@ static blk_status_t nvme_prep_rq(struct nvme_dev *dev, struct request *req)
 	blk_status_t ret;
 
 	iod->aborted = false;
-	iod->nr_descriptors = -1;
+	iod->nr_descriptors = 0;
+	iod->large_descriptors = false;
 	iod->sgt.nents = 0;
 
 	ret = nvme_setup_cmd(req->q->queuedata, req);
@@ -2694,7 +2688,8 @@ static int nvme_setup_prp_pools(struct nvme_dev *dev)
 
 	/* Optimisation for I/Os between 4k and 128k */
 	dev->prp_small_pool = dma_pool_create("prp list 256", dev->dev,
-						256, 256, 0);
+						NVME_SMALL_DESCRIPTOR_SIZE,
+						NVME_SMALL_DESCRIPTOR_SIZE, 0);
 	if (!dev->prp_small_pool) {
 		dma_pool_destroy(dev->prp_page_pool);
 		return -ENOMEM;
-- 
2.46.2