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([2620:10d:c092:600::1:2f22]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47fc89347bfsm4376944f8f.28.2026.07.30.03.41.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jul 2026 03:41:25 -0700 (PDT) Message-ID: Date: Thu, 30 Jul 2026 11:41:30 +0100 Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Pavel Begunkov Subject: Re: [PATCH v4 08/14] nvme-pci: implement dma_token backed requests To: Caleb Sander Mateos Cc: Jens Axboe , Keith Busch , Christoph Hellwig , Sagi Grimberg , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, Alexander Viro , Christian Brauner , Andrew Morton , Sumit Semwal , =?UTF-8?Q?Christian_K=C3=B6nig?= , Nitesh Shetty , Kanchan Joshi , Anuj Gupta , Tushar Gohad , William Power , Phil Cayton , Jason Gunthorpe , Damien Le Moal , Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski , Vishal Verma , David Sterba , Ilya Dryomov , dm-devel@lists.linux.dev, nvdimm@lists.linux.dev, linux-btrfs@vger.kernel.org, ceph-devel@vger.kernel.org References: <19e5c945ea8114320c10f7951d19197d48b59249.1785274111.git.asml.silence@gmail.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/29/26 20:43, Caleb Sander Mateos wrote: > On Tue, Jul 28, 2026 at 2:35 PM Pavel Begunkov wrote: >> >> Enable BIO_DMABUF_MAP backed requests. It creates a prp list for the >> dmabuf when it's mapped, which is then used to initialise requests. >> >> Suggested-by: Keith Busch >> Signed-off-by: Pavel Begunkov >> --- >> drivers/nvme/host/core.c | 12 ++ >> drivers/nvme/host/nvme.h | 2 + >> drivers/nvme/host/pci.c | 259 +++++++++++++++++++++++++++++++++++++++ >> 3 files changed, 273 insertions(+) >> >> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c >> index 453c1f0b2dd0..ce66a1843bec 100644 >> --- a/drivers/nvme/host/core.c >> +++ b/drivers/nvme/host/core.c >> @@ -2676,6 +2676,17 @@ static int nvme_report_zones(struct gendisk *disk, sector_t sector, >> #define nvme_report_zones NULL >> #endif /* CONFIG_BLK_DEV_ZONED */ >> >> +static int nvme_init_dma_buf_io_ctx(struct block_device *bdev, >> + struct dma_buf_io_ctx *ctx) >> +{ >> + struct nvme_ns *ns = bdev->bd_disk->private_data; >> + struct nvme_ctrl *ctrl = ns->ctrl; >> + >> + if (!ctrl->ops->init_dma_buf_io_ctx) >> + return -EINVAL; >> + return ctrl->ops->init_dma_buf_io_ctx(ctrl, ctx); >> +} >> + >> const struct block_device_operations nvme_bdev_ops = { >> .owner = THIS_MODULE, >> .ioctl = nvme_ioctl, >> @@ -2686,6 +2697,7 @@ const struct block_device_operations nvme_bdev_ops = { >> .get_unique_id = nvme_get_unique_id, >> .report_zones = nvme_report_zones, >> .pr_ops = &nvme_pr_ops, >> + .init_dma_buf_io_ctx = nvme_init_dma_buf_io_ctx, >> }; >> >> static int nvme_wait_ready(struct nvme_ctrl *ctrl, u32 mask, u32 val, >> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h >> index 824651cc898d..034c31af8fec 100644 >> --- a/drivers/nvme/host/nvme.h >> +++ b/drivers/nvme/host/nvme.h >> @@ -652,6 +652,8 @@ struct nvme_ctrl_ops { >> int (*get_address)(struct nvme_ctrl *ctrl, char *buf, int size); >> void (*print_device_info)(struct nvme_ctrl *ctrl); >> bool (*supports_pci_p2pdma)(struct nvme_ctrl *ctrl); >> + int (*init_dma_buf_io_ctx)(struct nvme_ctrl *ctrl, >> + struct dma_buf_io_ctx *ctx); >> unsigned long (*get_virt_boundary)(struct nvme_ctrl *ctrl, bool is_admin); >> }; >> >> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c >> index 69932d640b53..f1b67c191892 100644 >> --- a/drivers/nvme/host/pci.c >> +++ b/drivers/nvme/host/pci.c >> @@ -27,6 +27,8 @@ >> #include >> #include >> #include >> +#include >> +#include >> >> #include "trace.h" >> #include "nvme.h" >> @@ -393,6 +395,13 @@ struct nvme_queue { >> struct completion delete_done; >> }; >> >> +struct nvme_dmabuf_map { >> + struct dma_buf_io_map base; >> + struct sg_table *sgt; >> + unsigned nr_entries; >> + dma_addr_t dma_list[]; >> +}; >> + >> /* bits for iod->flags */ >> enum nvme_iod_flags { >> /* this command has been aborted by the timeout handler */ >> @@ -859,6 +868,138 @@ static void nvme_free_descriptors(struct request *req) >> } >> } >> >> +static inline struct nvme_dmabuf_map * >> +to_nvme_dmabuf_map(struct dma_buf_io_map *map) >> +{ >> + return container_of(map, struct nvme_dmabuf_map, base); >> +} >> + >> +static void nvme_dmabuf_map_sync_for_cpu(struct nvme_dev *nvme_dev, >> + struct request *req) >> +{ >> + struct device *dev = nvme_dev->dev; >> + enum dma_data_direction dma_dir; >> + struct bio *bio = req->bio; >> + struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map); >> + dma_addr_t *dma_list = map->dma_list; >> + unsigned offset = bio->bi_iter.bi_offset; >> + unsigned map_idx = offset / NVME_CTRL_PAGE_SIZE; >> + int length = blk_rq_payload_bytes(req) + >> + (offset & (NVME_CTRL_PAGE_SIZE - 1)); >> + >> + dma_dir = rq_data_dir(req) == READ ? DMA_FROM_DEVICE : DMA_TO_DEVICE; >> + >> + while (length > 0) { >> + dma_sync_single_for_cpu(dev, dma_list[map_idx++], >> + NVME_CTRL_PAGE_SIZE, dma_dir); >> + length -= NVME_CTRL_PAGE_SIZE; >> + } >> +} >> + >> +static void nvme_dmabuf_map_sync_for_device(struct nvme_dev *nvme_dev, >> + struct request *req) >> +{ >> + struct device *dev = nvme_dev->dev; >> + enum dma_data_direction dma_dir; >> + struct bio *bio = req->bio; >> + struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map); >> + dma_addr_t *dma_list = map->dma_list; >> + unsigned offset = bio->bi_iter.bi_offset; >> + unsigned map_idx = offset / NVME_CTRL_PAGE_SIZE; >> + int length = blk_rq_payload_bytes(req) + >> + (offset & (NVME_CTRL_PAGE_SIZE - 1)); >> + >> + dma_dir = rq_data_dir(req) == READ ? DMA_FROM_DEVICE : DMA_TO_DEVICE; >> + >> + while (length > 0) { >> + dma_sync_single_for_device(dev, dma_list[map_idx++], >> + NVME_CTRL_PAGE_SIZE, dma_dir); >> + length -= NVME_CTRL_PAGE_SIZE; >> + } >> +} >> + >> +static void nvme_rq_clean_dmabuf_map(struct nvme_dev *dev, >> + struct request *req) >> +{ >> + struct nvme_iod *iod = blk_mq_rq_to_pdu(req); >> + >> + nvme_dmabuf_map_sync_for_cpu(dev, req); >> + >> + if (!(iod->flags & IOD_SINGLE_SEGMENT)) >> + nvme_free_descriptors(req); >> +} >> + >> +static blk_status_t nvme_rq_setup_dmabuf_map(struct request *req, >> + struct nvme_queue *nvmeq) >> +{ >> + struct nvme_iod *iod = blk_mq_rq_to_pdu(req); >> + struct bio *bio = req->bio; >> + struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map); >> + unsigned bvec_done = bio->bi_iter.bi_offset; >> + unsigned map_idx = bvec_done / NVME_CTRL_PAGE_SIZE; >> + unsigned offset = bvec_done & (NVME_CTRL_PAGE_SIZE - 1); >> + int length = blk_rq_payload_bytes(req) - (NVME_CTRL_PAGE_SIZE - offset); >> + dma_addr_t *dma_list = map->dma_list; >> + u64 prp1_dma = dma_list[map_idx++] + offset; >> + u64 dma_addr, prp2_dma; >> + dma_addr_t prp_dma; >> + __le64 *prp_list; >> + unsigned i; >> + >> + nvme_dmabuf_map_sync_for_device(nvmeq->dev, req); >> + >> + if (length <= 0) { >> + prp2_dma = 0; >> + goto done; >> + } >> + >> + if (length <= NVME_CTRL_PAGE_SIZE) { >> + prp2_dma = dma_list[map_idx]; >> + goto done; >> + } >> + >> + if (DIV_ROUND_UP(length, NVME_CTRL_PAGE_SIZE) <= >> + NVME_SMALL_POOL_SIZE / sizeof(__le64)) >> + iod->flags |= IOD_SMALL_DESCRIPTOR; >> + >> + prp_list = dma_pool_alloc(nvme_dma_pool(nvmeq, iod), GFP_ATOMIC, >> + &prp_dma); > > I wonder if it's possible to perform the PRP list page allocations and > initialization in nvme_dma_buf_io_map() instead of the I/O path. The > NVMe dma_pools are per-NUMA-node linked lists protected by spinlocks, > making them significant CPU hotspots. If the dmabuf registration set > up a contiguous DMA-coherent list of PRP entries for the pages of the > registered buffer, any command using the dmabuf and requiring at most > 1 PRP list page (i.e. length <= 2 MB) could just set its PRP list > pointer to an offset into the dmabuf's PRP list. Possible to an extent, predecessor patches tried that, I left it for later to keep the series simpler. I guess chaining won't work in general case. I mentioned this to Kanchan, Anuj and Nitesh before, they were up to playing with nvme optimisations in general, and since sgl from Anuj is ready, maybe they already have a prototype somewhere for that. -- Pavel Begunkov