Re: [RFC PATCHv4 1/3] nvme-multipath: introduce delayed removal of the multipath head node

[Hannes Reinecke <hare@suse.de>]

On 5/9/25 19:51, Nilay Shroff wrote:
> Currently, the multipath head node of an NVMe disk is removed
> immediately as soon as all paths of the disk are removed. However,
> this can cause issues in scenarios where:
> 
> - The disk hot-removal followed by re-addition.
> - Transient PCIe link failures that trigger re-enumeration,
>    temporarily removing and then restoring the disk.
> 
> In these cases, removing the head node prematurely may lead to a head
> disk node name change upon re-addition, requiring applications to
> reopen their handles if they were performing I/O during the failure.
> 
> To address this, introduce a delayed removal mechanism of head disk
> node. During transient failure, instead of immediate removal of head
> disk node, the system waits for a configurable timeout, allowing the
> disk to recover.
> 
> During transient disk failure, if application sends any IO then we
> queue it instead of failing such IO immediately. If the disk comes back
> online within the timeout, the queued IOs are resubmitted to the disk
> ensuring seamless operation. In case disk couldn't recover from the
> failure then queued IOs are failed to its completion and application
> receives the error.
> 
> So this way, if disk comes back online within the configured period,
> the head node remains unchanged, ensuring uninterrupted workloads
> without requiring applications to reopen device handles.
> 
> A new sysfs attribute, named "delayed_removal_secs" is added under head
> disk blkdev for user who wish to configure time for the delayed removal
> of head disk node. The default value of this attribute is set to zero
> second ensuring no behavior change unless explicitly configured.
> 
> Link: https://lore.kernel.org/linux-nvme/Y9oGTKCFlOscbPc2@infradead.org/
> Link: https://lore.kernel.org/linux-nvme/Y+1aKcQgbskA2tra@kbusch-mbp.dhcp.thefacebook.com/
> Suggested-by: Keith Busch <kbusch@kernel.org>
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> [nilay: reworked based on the original idea/POC from Christoph and Keith]
> Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
> ---
>   drivers/nvme/host/core.c      |   8 ++-
>   drivers/nvme/host/multipath.c | 130 +++++++++++++++++++++++++++++++---
>   drivers/nvme/host/nvme.h      |  16 ++++-
>   drivers/nvme/host/sysfs.c     |   7 ++
>   4 files changed, 147 insertions(+), 14 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
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