[PATCH 4/7] nvme: export I/O requeue count when no path is available via sysfs

Nilay Shroff
2026-01-30T18:21:18Z

When the NVMe namespace head determines that there is no currently
available path to handle I/O (for example, while a controller is
resetting/connecting or due to a transient link failure), incoming
I/Os are added to the requeue list.

Currently, there is no visibility into how many I/Os have been requeued
in this situation. Add a new sysfs counter, requeue_no_available_path,
to expose the number of I/Os that were requeued due to the absence of
an available path.

This statistic can help users understand I/O slowdowns or stalls caused
by temporary path unavailability, and can be consumed by monitoring
tools such as nvme-top for real-time observability.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
---
drivers/nvme/host/multipath.c | 11 +++++++++++
drivers/nvme/host/nvme.h | 2 ++
drivers/nvme/host/sysfs.c | 5 +++++
3 files changed, 18 insertions(+)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 366b820e654a..4e5f8523ca40 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -539,6 +539,7 @@ static void nvme_ns_head_submit_bio(struct bio *bio)
spin_lock_irq(&head->requeue_lock);
bio_list_add(&head->requeue_list, bio);
spin_unlock_irq(&head->requeue_lock);
+ head->requeue_no_usable_path++;
} else {
dev_warn_ratelimited(dev, "no available path - failing I/O\n");

@@ -1178,6 +1179,16 @@ static ssize_t multipath_failover_count_show(struct device *dev,
}
DEVICE_ATTR_RO(multipath_failover_count);

+static ssize_t requeue_no_usable_path_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct gendisk *disk = dev_to_disk(dev);
+ struct nvme_ns_head *head = disk->private_data;
+
+ return sysfs_emit(buf, "%llu\n", head->requeue_no_usable_path);
+}
+DEVICE_ATTR_RO(requeue_no_usable_path);
+
static int nvme_lookup_ana_group_desc(struct nvme_ctrl *ctrl,
struct nvme_ana_group_desc *desc, void *data)
{
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index b7e46bdd2d59..5836e4c557a2 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -509,6 +509,7 @@ struct nvme_ns_head {
unsigned long flags;
struct delayed_work remove_work;
unsigned int delayed_removal_secs;
+ u64 requeue_no_usable_path;
#define NVME_NSHEAD_DISK_LIVE 0
#define NVME_NSHEAD_QUEUE_IF_NO_PATH 1
struct nvme_ns __rcu *current_path[];
@@ -1005,6 +1006,7 @@ extern struct device_attribute dev_attr_queue_depth;
extern struct device_attribute dev_attr_numa_nodes;
extern struct device_attribute dev_attr_delayed_removal_secs;
extern struct device_attribute dev_attr_multipath_failover_count;
+extern struct device_attribute dev_attr_requeue_no_usable_path;
extern struct device_attribute subsys_attr_iopolicy;

static inline bool nvme_disk_is_ns_head(struct gendisk *disk)
diff --git a/drivers/nvme/host/sysfs.c b/drivers/nvme/host/sysfs.c
index 41218fa5081f..84d33445a578 100644
--- a/drivers/nvme/host/sysfs.c
+++ b/drivers/nvme/host/sysfs.c
@@ -284,6 +284,7 @@ static struct attribute *nvme_ns_attrs[] = {
&dev_attr_numa_nodes.attr,
&dev_attr_delayed_removal_secs.attr,
&dev_attr_multipath_failover_count.attr,
+ &dev_attr_requeue_no_usable_path.attr,
#endif
&dev_attr_io_passthru_err_log_enabled.attr,
&dev_attr_io_command_retries.attr,
@@ -344,6 +345,10 @@ static umode_t nvme_ns_attrs_are_visible(struct kobject *kobj,
if (nvme_disk_is_ns_head(dev_to_disk(dev)))
return 0;
}
+ if (a == &dev_attr_requeue_no_usable_path.attr) {
+ if (!nvme_disk_is_ns_head(dev_to_disk(dev)))
+ return 0;
+ }
#endif
return a->mode;
}
--
2.52.0