[PATCH 2/2] nvmet: add file-backed ns write-through support

[Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>]

This patch adds a new configfs parameter "write_through" which allows
user to optionally write through I/O. This approach increases
performance for I/O workloads like 70% read and 30% write where
applications are mostly dealing with write once and read many times
scenario e.g. social media posts, pictures. This also avoids cost of
round trip required for read operation when buffered-io is enabled to
populate the cache when the dataset is large and distributed among
namespaces residing on different controllers with different targets.

Cc: hch@lst.de
Cc: sagi@grimberg.me
Cc: MRuijter@onestopsystems.com

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
---
 drivers/nvme/target/configfs.c    | 30 ++++++++++++++++++++++++++++++
 drivers/nvme/target/io-cmd-file.c | 16 ++++++++++++----
 drivers/nvme/target/nvmet.h       |  9 +++++++++
 3 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index 500cacfc715c..70477343f194 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -584,6 +584,35 @@ static ssize_t nvmet_ns_backend_store(struct config_item *item,
 
 CONFIGFS_ATTR(nvmet_ns_, backend);
 
+static ssize_t nvmet_ns_write_through_show(struct config_item *item,
+		char *page)
+{
+	return sprintf(page, "%d\n", to_nvmet_ns(item)->write_through);
+}
+
+static ssize_t nvmet_ns_write_through_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct nvmet_ns *ns = to_nvmet_ns(item);
+	bool val;
+
+	if (strtobool(page, &val))
+		return -EINVAL;
+
+	mutex_lock(&ns->subsys->lock);
+	if (ns->enabled) {
+		pr_err("disable ns before setting write_through value.\n");
+		mutex_unlock(&ns->subsys->lock);
+		return -EBUSY;
+	}
+
+	ns->write_through = val;
+	mutex_unlock(&ns->subsys->lock);
+	return count;
+}
+
+CONFIGFS_ATTR(nvmet_ns_, write_through);
+
 static struct configfs_attribute *nvmet_ns_attrs[] = {
 	&nvmet_ns_attr_device_path,
 	&nvmet_ns_attr_device_nguid,
@@ -592,6 +621,7 @@ static struct configfs_attribute *nvmet_ns_attrs[] = {
 	&nvmet_ns_attr_enable,
 	&nvmet_ns_attr_buffered_io,
 	&nvmet_ns_attr_backend,
+	&nvmet_ns_attr_write_through,
 #ifdef CONFIG_PCI_P2PDMA
 	&nvmet_ns_attr_p2pmem,
 #endif
diff --git a/drivers/nvme/target/io-cmd-file.c b/drivers/nvme/target/io-cmd-file.c
index 8a642cda123d..4ac306419177 100644
--- a/drivers/nvme/target/io-cmd-file.c
+++ b/drivers/nvme/target/io-cmd-file.c
@@ -35,8 +35,10 @@ int nvmet_file_ns_enable(struct nvmet_ns *ns)
 	struct kstat stat;
 	int ret;
 
-	if (!ns->buffered_io)
+	if (nvmet_file_ns_is_direct_io(ns))
 		flags |= O_DIRECT;
+	else if (!ns->buffered_io && ns->write_through)
+		flags |= O_DSYNC;
 
 	ns->file = filp_open(ns->device_path, flags, 0);
 	if (IS_ERR(ns->file)) {
@@ -198,7 +200,7 @@ static bool nvmet_file_execute_io(struct nvmet_req *req, int ki_flags)
 	 * A NULL ki_complete ask for synchronous execution, which we want
 	 * for the IOCB_NOWAIT case.
 	 */
-	if (!(ki_flags & IOCB_NOWAIT))
+	if (!((ki_flags & IOCB_NOWAIT) || (ki_flags & IOCB_SYNC)))
 		req->f.iocb.ki_complete = nvmet_file_io_done;
 
 	ret = nvmet_file_submit_bvec(req, pos, bv_cnt, total_len, ki_flags);
@@ -229,8 +231,12 @@ static bool nvmet_file_execute_io(struct nvmet_req *req, int ki_flags)
 static void nvmet_file_buffered_io_work(struct work_struct *w)
 {
 	struct nvmet_req *req = container_of(w, struct nvmet_req, f.work);
+	int write_sync = 0;
 
-	nvmet_file_execute_io(req, 0);
+	if (req->cmd->common.opcode == nvme_cmd_write && req->ns->write_through)
+		write_sync = IOCB_SYNC;
+
+	nvmet_file_execute_io(req, write_sync);
 }
 
 static void nvmet_file_submit_buffered_io(struct nvmet_req *req)
@@ -264,8 +270,10 @@ static void nvmet_file_execute_rw(struct nvmet_req *req)
 	} else
 		req->f.mpool_alloc = false;
 
-	if (req->ns->buffered_io) {
+	if (req->ns->buffered_io || req->ns->write_through) {
 		if (likely(!req->f.mpool_alloc) &&
+				req->ns->buffered_io &&
+				!req->ns->write_through &&
 				nvmet_file_execute_io(req, IOCB_NOWAIT))
 			return;
 		nvmet_file_submit_buffered_io(req);
diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
index d78d9990e513..815096728dc6 100644
--- a/drivers/nvme/target/nvmet.h
+++ b/drivers/nvme/target/nvmet.h
@@ -69,6 +69,7 @@ struct nvmet_ns {
 	u32			anagrpid;
 
 	bool			buffered_io;
+	bool                    write_through;
 	bool			enabled;
 	struct nvmet_subsys	*subsys;
 	const char		*device_path;
@@ -516,6 +517,14 @@ static inline u32 nvmet_dsm_len(struct nvmet_req *req)
 		sizeof(struct nvme_dsm_range);
 }
 
+static inline bool nvmet_file_ns_is_direct_io(struct nvmet_ns *ns)
+{
+	if (!(ns->buffered_io || ns->write_through))
+		return true;
+
+	return false;
+}
+
 u16 errno_to_nvme_status(struct nvmet_req *req, int errno);
 
 /* Convert a 32-bit number to a 16-bit 0's based number */
-- 
2.22.1


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