Re: [PATCH v8 13/13] nvmet: Optionally use PCI P2P memory

Sagi Grimberg
2018-10-01T21:34:28Z

On 09/27/2018 09:54 AM, Logan Gunthorpe wrote:
> We create a configfs attribute in each nvme-fabrics target port to
> enable p2p memory use. When enabled, the port will only then use the
> p2p memory if a p2p memory device can be found which is behind the
> same switch hierarchy as the RDMA port and all the block devices in
> use. If the user enabled it and no devices are found, then the system
> will silently fall back on using regular memory.
>
> If appropriate, that port will allocate memory for the RDMA buffers
> for queues from the p2pmem device falling back to system memory should
> anything fail.
>
> Ideally, we'd want to use an NVME CMB buffer as p2p memory. This would
> save an extra PCI transfer as the NVME card could just take the data
> out of it's own memory. However, at this time, only a limited number
> of cards with CMB buffers seem to be available.
>
> Signed-off-by: Stephen Bates <sbates@raithlin.com>
> Signed-off-by: Steve Wise <swise@opengridcomputing.com>
> [hch: partial rewrite of the initial code]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> ---
> drivers/nvme/target/configfs.c | 36 ++++++++
> drivers/nvme/target/core.c | 138 +++++++++++++++++++++++++++++-
> drivers/nvme/target/io-cmd-bdev.c | 3 +
> drivers/nvme/target/nvmet.h | 13 +++
> drivers/nvme/target/rdma.c | 2 +
> 5 files changed, 191 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
> index b37a8e3e3f80..0dfb0e0c3d21 100644
> --- a/drivers/nvme/target/configfs.c
> +++ b/drivers/nvme/target/configfs.c
> @@ -17,6 +17,8 @@
> #include <linux/slab.h>
> #include <linux/stat.h>
> #include <linux/ctype.h>
> +#include <linux/pci.h>
> +#include <linux/pci-p2pdma.h>
>
> #include "nvmet.h"
>
> @@ -1094,6 +1096,37 @@ static void nvmet_port_release(struct config_item *item)
> kfree(port);
> }
>
> +#ifdef CONFIG_PCI_P2PDMA
> +static ssize_t nvmet_p2pmem_show(struct config_item *item, char *page)
> +{
> + struct nvmet_port *port = to_nvmet_port(item);
> +
> + return pci_p2pdma_enable_show(page, port->p2p_dev, port->use_p2pmem);
> +}
> +
> +static ssize_t nvmet_p2pmem_store(struct config_item *item,
> + const char *page, size_t count)
> +{
> + struct nvmet_port *port = to_nvmet_port(item);
> + struct pci_dev *p2p_dev = NULL;
> + bool use_p2pmem;
> + int error;
> +
> + error = pci_p2pdma_enable_store(page, &p2p_dev, &use_p2pmem);
> + if (error)
> + return error;
> +
> + down_write(&nvmet_config_sem);
> + port->use_p2pmem = use_p2pmem;
> + pci_dev_put(port->p2p_dev);
> + port->p2p_dev = p2p_dev;
> + up_write(&nvmet_config_sem);
> +
> + return count;
> +}
> +CONFIGFS_ATTR(nvmet_, p2pmem);
> +#endif /* CONFIG_PCI_P2PDMA */
> +
> static struct configfs_attribute *nvmet_port_attrs[] = {
> &nvmet_attr_addr_adrfam,
> &nvmet_attr_addr_treq,
> @@ -1101,6 +1134,9 @@ static struct configfs_attribute *nvmet_port_attrs[] = {
> &nvmet_attr_addr_trsvcid,
> &nvmet_attr_addr_trtype,
> &nvmet_attr_param_inline_data_size,
> +#ifdef CONFIG_PCI_P2PDMA
> + &nvmet_attr_p2pmem,
> +#endif
> NULL,
> };
>
> diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
> index bddd1599b826..7ade16cb4ed3 100644
> --- a/drivers/nvme/target/core.c
> +++ b/drivers/nvme/target/core.c
> @@ -15,6 +15,7 @@
> #include <linux/module.h>
> #include <linux/random.h>
> #include <linux/rculist.h>
> +#include <linux/pci-p2pdma.h>
>
> #include "nvmet.h"
>
> @@ -365,9 +366,29 @@ static void nvmet_ns_dev_disable(struct nvmet_ns *ns)
> nvmet_file_ns_disable(ns);
> }
>
> +static int nvmet_p2pdma_add_client(struct nvmet_ctrl *ctrl,
> + struct nvmet_ns *ns)
> +{
> + int ret;
> +
> + if (!blk_queue_pci_p2pdma(ns->bdev->bd_queue)) {
> + pr_err("peer-to-peer DMA is not supported by %s\n",
> + ns->device_path);
> + return -EINVAL;
> + }
> +
> + ret = pci_p2pdma_add_client(&ctrl->p2p_clients, nvmet_ns_dev(ns));
> + if (ret)
> + pr_err("failed to add peer-to-peer DMA client %s: %d\n",
> + ns->device_path, ret);
> +
> + return ret;
> +}
> +
> int nvmet_ns_enable(struct nvmet_ns *ns)
> {
> struct nvmet_subsys *subsys = ns->subsys;
> + struct nvmet_ctrl *ctrl;
> int ret;
>
> mutex_lock(&subsys->lock);
> @@ -389,6 +410,14 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
> if (ret)
> goto out_dev_put;
>
> + list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
> + if (ctrl->p2p_dev) {
> + ret = nvmet_p2pdma_add_client(ctrl, ns);
> + if (ret)
> + goto out_remove_clients;
> + }
> + }
> +
> if (ns->nsid > subsys->max_nsid)
> subsys->max_nsid = ns->nsid;
>
> @@ -417,6 +446,9 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
> out_unlock:
> mutex_unlock(&subsys->lock);
> return ret;
> +out_remove_clients:
> + list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry)
> + pci_p2pdma_remove_client(&ctrl->p2p_clients, nvmet_ns_dev(ns));
> out_dev_put:
> nvmet_ns_dev_disable(ns);
> goto out_unlock;
> @@ -425,6 +457,7 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
> void nvmet_ns_disable(struct nvmet_ns *ns)
> {
> struct nvmet_subsys *subsys = ns->subsys;
> + struct nvmet_ctrl *ctrl;
>
> mutex_lock(&subsys->lock);
> if (!ns->enabled)
> @@ -450,6 +483,12 @@ void nvmet_ns_disable(struct nvmet_ns *ns)
> percpu_ref_exit(&ns->ref);
>
> mutex_lock(&subsys->lock);
> +
> + list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
> + pci_p2pdma_remove_client(&ctrl->p2p_clients, nvmet_ns_dev(ns));
> + nvmet_add_async_event(ctrl, NVME_AER_TYPE_NOTICE, 0, 0);

Hi Logan, what is this event here?

> + }
> +
> subsys->nr_namespaces--;
> nvmet_ns_changed(subsys, ns->nsid);
> nvmet_ns_dev_disable(ns);
> @@ -727,6 +766,23 @@ EXPORT_SYMBOL_GPL(nvmet_req_execute);
>
> int nvmet_req_alloc_sgl(struct nvmet_req *req, struct nvmet_sq *sq)
> {
> + struct pci_dev *p2p_dev = NULL;
> +
> + if (IS_ENABLED(CONFIG_PCI_P2PDMA)) {
> + if (sq->ctrl)
> + p2p_dev = sq->ctrl->p2p_dev;
> +
> + req->p2p_dev = NULL;
> + if (sq->qid && p2p_dev) {
> + req->sg = pci_p2pmem_alloc_sgl(p2p_dev, &req->sg_cnt,
> + req->transfer_len);
> + if (req->sg) {
> + req->p2p_dev = p2p_dev;
> + return 0;
> + }

Would be useful to comment that we fall to normal sgl allocation.

> + }
> + }
> +
> req->sg = sgl_alloc(req->transfer_len, GFP_KERNEL, &req->sg_cnt);
> if (!req->sg)
> return -ENOMEM;
> @@ -737,7 +793,11 @@ EXPORT_SYMBOL_GPL(nvmet_req_alloc_sgl);
>
> void nvmet_req_free_sgl(struct nvmet_req *req)
> {
> - sgl_free(req->sg);
> + if (req->p2p_dev)
> + pci_p2pmem_free_sgl(req->p2p_dev, req->sg);
> + else
> + sgl_free(req->sg);
> +
> req->sg = NULL;
> req->sg_cnt = 0;
> }
> @@ -939,6 +999,79 @@ bool nvmet_host_allowed(struct nvmet_req *req, struct nvmet_subsys *subsys,
> return __nvmet_host_allowed(subsys, hostnqn);
> }
>
> +/*
> + * If allow_p2pmem is set, we will try to use P2P memory for the SGL lists for
> + * Ι/O commands. This requires the PCI p2p device to be compatible with the
> + * backing device for every namespace on this controller.
> + */
> +static void nvmet_setup_p2pmem(struct nvmet_ctrl *ctrl, struct nvmet_req *req)
> +{
> + struct nvmet_ns *ns;
> + int ret;
> +
> + if (!req->port->use_p2pmem || !req->p2p_client)
> + return;

Nit, IMO would be better to check at the call-site, but not a hard
must...

I still do not fully understand why p2p_dev has to be ctrl-wide and not
per namespace. Sorry to keep bringing this up (again). But if people are
OK with it then I guess I can stop asking about this...

> +
> + mutex_lock(&ctrl->subsys->lock);
> +
> + ret = pci_p2pdma_add_client(&ctrl->p2p_clients, req->p2p_client);
> + if (ret) {
> + pr_err("failed adding peer-to-peer DMA client %s: %d\n",
> + dev_name(req->p2p_client), ret);
> + goto free_devices;
> + }
> +
> + list_for_each_entry_rcu(ns, &ctrl->subsys->namespaces, dev_link) {
> + ret = nvmet_p2pdma_add_client(ctrl, ns);
> + if (ret)
> + goto free_devices;

I think that at some point we said that this looks like it should fall
back to host memory for those namespaces.. when we allocate the sgl we
already assigned a namespace to the request (nvmet_req_init).

Aside from my questions the patch looks good.