Hi, This patch series introduces improvements to NVMe multipath handling by refining the removal behavior of the multipath head node and simplifying configuration options. The idea/POC for this change was originally proposed by Christoph[1] and Keith[2]. I worked upon their original idea/POC and implemented this series. The first patch in the series addresses an issue where the multipath head node of a PCIe NVMe disk is removed immediately when all disk paths are lost. This can cause problems in scenarios such as: - Hot removal and re-addition of a disk. - Transient PCIe link failures that trigger re-enumeration, briefly removing and restoring the disk. In such cases, premature removal of the head node may result in a device node name change, requiring applications to reopen device handles if they were performing I/O during the failure. To mitigate this, we introduce a delayed removal mechanism. Instead of removing the head node immediately, the system waits for a configurable timeout, allowing the disk to recover. If the disk comes back online within this window, the head node remains unchanged, ensuring uninterrupted workloads. A new sysfs attribute, delayed_shutdown_sec, allows users to configure this timeout. By default, it is set to 0 seconds, preserving the existing behavior unless explicitly changed. Additionally, please note that this change now always creates head disk node for all types of NVMe disks (single-ported or multi-ported) as well as shared/private namespaces, unless the multipath nvme-core module parameter is explicitly set to false or CONFIG_NVME_MULTIPATH is disabled. The second patch removes the multipath module parameter parameter from nvme-core, making native NVMe multipath support explicit. Now with first patch changes, the multipath head node is always created, even for single- port NVMe disks when CONFIG_NVME_MULTIPATH is configured. Since this behavior is now default, the multipath module parameter may no longer be needed. IMO, the CONFIG_NVME_MULTIPATH (native-multipath) should be the default and non-native multipath should ideally be deprecated by now, however I didn't remove CONFIG_NVME_MULTIPATH in this series. So users who still prefers non-native multipath can disable CONFIG_NVME_MULTIPATH at compile time. Having said that, if everyone agress we may depreacte non-native multipath support for NVMe. These changes should help improve NVMe multipath reliability and simplify configuration. Feedback and testing are welcome! PS: Yes I know this RFC is late, but the intention is to get feedback/ suggestion in the upcoming LSF/MM/BPF summit. This might be used as a reference implementation for discussion. I also saw that we've already got a timeslot where John is going to talk about removing NVMe multipath config option. Maybe we could include it in that discussion, if everyone agress. Thanks! --Nilay Nilay Shroff (2): nvme-multipath: introduce delayed removal of the multipath head node nvme-multipath: remove multipath module param drivers/nvme/host/core.c | 36 ++++------ drivers/nvme/host/multipath.c | 127 ++++++++++++++++++++++++++-------- drivers/nvme/host/nvme.h | 5 +- drivers/nvme/host/sysfs.c | 13 ++++ 4 files changed, 132 insertions(+), 49 deletions(-) -- 2.47.1
